{"gene":"SND1","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":1998,"finding":"Pim-1 kinase was found to interact with p100 (SND1) via yeast two-hybrid screen; Pim-1 phosphorylated p100 in vitro, formed a stable complex with p100 in animal cells, and functioned downstream of Ras to stimulate c-Myb transcriptional activity in a p100-dependent manner, establishing p100/SND1 as a transcriptional coactivator linking cytokine signaling to c-Myb activity.","method":"Yeast two-hybrid screen, in vitro phosphorylation assay, co-immunoprecipitation, transactivation assay","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Y2H, in vitro kinase assay, co-IP, transcriptional reporter) in single study","pmids":["9809063"],"is_preprint":false},{"year":2002,"finding":"p100/SND1 was identified as a coactivator for STAT6 that bridges STAT6 with RNA polymerase II. The interaction was mediated by the TAD domain of STAT6 and the SN-like domain of p100. p100 enhanced STAT6-mediated transcriptional activation and IL-4-induced Igε gene transcription, and associated with the large subunit of RNA polymerase II.","method":"Co-immunoprecipitation, in vitro interaction assay, reporter gene assay, domain mapping","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus in vitro binding, domain mapping, and functional reporter assay","pmids":["12234934"],"is_preprint":false},{"year":2007,"finding":"The TSN domain of p100/SND1 specifically interacts with components of the U5 snRNP and other spliceosomal snRNPs. Purified p100 and its isolated TSN domain accelerated spliceosome complex A formation and the A-to-B transition in vitro, and enhanced the kinetics of the first splicing step in a dose-dependent manner, revealing a dual role in transcription and pre-mRNA splicing.","method":"Co-immunoprecipitation, in vitro splicing assay, domain-specific pull-down","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstituted splicing assay with purified protein, domain-specific functional dissection","pmids":["17576664"],"is_preprint":false},{"year":2007,"finding":"Crystal structure of the p100/SND1 TSN domain was determined, revealing an interdigitated hook-like structure with a conserved aromatic cage that hooks methyl groups of snRNP proteins, providing structural explanation for SND1's roles in transcription and spliceosome anchoring.","method":"X-ray crystallography, structural analysis of Tudor-SN domain with snRNP peptides","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with functional validation","pmids":["17632523"],"is_preprint":false},{"year":2007,"finding":"SND1 was identified as a component of the RNA-induced silencing complex (RISC) and was shown to be up-regulated in human colon cancers. Overexpression of SND1 in intestinal epithelial cells caused loss of contact inhibition, promoted cell growth, altered E-cadherin distribution, and down-regulated APC protein (without altering APC mRNA), implicating SND1-mediated post-transcriptional regulation in colon carcinogenesis.","method":"Stable overexpression, cell proliferation assay, immunofluorescence, Western blot, immunohistochemistry","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2-3 — overexpression with defined cellular phenotype and molecular readout (APC protein loss without mRNA change), single lab","pmids":["17909068"],"is_preprint":false},{"year":2008,"finding":"p100/SND1 was found to bind the angiotensin II type 1 receptor (AT1R) 3'-UTR via its SN-like domains, increasing AT1R expression by decreasing mRNA decay rate and enhancing translation. This effect was independent of Argonaute2/RISC, revealing a novel mRNA-stabilizing function of SND1.","method":"RNA pull-down, p100 silencing, overexpression, mRNA decay assay, deletion mapping of binding site","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — RNA binding mapped to specific domain, functional consequence on mRNA stability and translation, RISC-independent mechanism demonstrated","pmids":["18603592"],"is_preprint":false},{"year":2010,"finding":"Cellular p100/SND1 was identified as a host factor that binds the dengue virus 3'-UTR (specifically the A4 stem-loop region). p100 knockdown reduced viral RNA levels and viral protein expression, and decreased expression of a luciferase-3'UTR(DENV) reporter in an A4-dependent manner, demonstrating that SND1 is required for normal dengue virus replication.","method":"RNA affinity capture, mass spectrometry, RNA immunoprecipitation, confocal immunofluorescence, siRNA knockdown, luciferase reporter assay","journal":"The Journal of general virology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods confirming RNA binding and functional requirement in viral replication","pmids":["21148275"],"is_preprint":false},{"year":2011,"finding":"SND1 was identified as a MTDH (Metadherin)-interacting protein by mass spectrometry-based screen. SND1 strongly promotes lung metastasis in breast cancer models and promotes resistance to apoptosis. Silencing SND1 reduced metastatic potential and regulated expression of genes associated with metastasis and chemoresistance.","method":"Mass spectrometry interactome screen, co-immunoprecipitation, shRNA knockdown, in vivo metastasis assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — MS-based interaction confirmed by co-IP, loss-of-function with in vivo phenotype","pmids":["21478147"],"is_preprint":false},{"year":2013,"finding":"SND1 was found to interact with SAM68 in prostate cancer cells. SND1 upregulation synergizes with SAM68 to promote inclusion of CD44 variable exons. SND1 promotes inclusion of CD44 variable exons by recruiting SAM68 and spliceosomal components to CD44 pre-mRNA. Knockdown of SND1 reduced proliferation and migration of prostate cancer cells.","method":"Mass spectrometry, co-immunoprecipitation, RNA immunoprecipitation, siRNA knockdown, alternative splicing analysis, cell migration/proliferation assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal co-IP, RIP, functional splicing analysis, and loss-of-function phenotype","pmids":["23995791"],"is_preprint":false},{"year":2014,"finding":"High-resolution crystal structure of the MTDH-SND1 complex was determined, revealing that an 11-residue MTDH peptide motif occupies an extended groove between SND1's SN1/2 domains, with two MTDH tryptophan residues nestled into two pockets in SND1. Mutations at both tryptophan-binding pockets impaired MTDH-SND1 interactions and their roles in breast cancer, and also impaired SND1 stability under stress.","method":"X-ray crystallography, site-directed mutagenesis, co-immunoprecipitation, cancer cell functional assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with mutagenesis validation and functional phenotype","pmids":["25242325"],"is_preprint":false},{"year":2014,"finding":"MTDH-SND1 interaction is crucial for expansion and activity of tumor-initiating cells (TICs) in mammary tumors. Mechanistically, MTDH supports survival of mammary epithelial cells under oncogenic/stress conditions by interacting with and stabilizing SND1. Silencing MTDH or SND1 individually, or disrupting their interaction, compromised tumorigenic potential of TICs in vivo.","method":"Mouse mammary tumor models, genetic knockdown, co-immunoprecipitation, tumor-initiating cell assays in vivo","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 — multiple mouse models, genetic ablation with defined mechanistic readout, in vivo validation","pmids":["24981741"],"is_preprint":false},{"year":2015,"finding":"SND1 acts downstream of TGFβ1 and upstream of Smurf1 to promote breast cancer metastasis. TGFβ1/Smad2/Smad3 complex transcriptionally activates SND1 via Smad recognition domains (RD motifs) in the SND1 promoter. SND1 promotes Smurf1 expression, leading to RhoA ubiquitination and degradation, disrupting F-actin organization, reducing cell adhesion, and increasing cell migration and invasion.","method":"Promoter analysis, ChIP, reporter assay, co-immunoprecipitation, siRNA knockdown, cell migration/invasion assays, in vivo metastasis model","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 — epistasis established by pathway analysis with multiple orthogonal methods including ChIP, co-IP, and in vivo model","pmids":["25596283"],"is_preprint":false},{"year":2016,"finding":"SND1 promotes hepatocarcinogenesis by interacting with and inducing ubiquitination and proteasomal degradation of monoglyceride lipase (MGLL), a tumor suppressor. MGLL overexpression inhibited HCC cell proliferation and tumor growth, and inhibited Akt activation independently of MGLL's enzymatic activity.","method":"Yeast two-hybrid assay, co-immunoprecipitation, ubiquitination assay, cell proliferation assay, in vivo xenograft assay, IHC of tissue microarray","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — Y2H confirmed by co-IP, ubiquitination mechanism established, in vivo functional validation","pmids":["26997225"],"is_preprint":false},{"year":2017,"finding":"SND1 physically associates with and recruits the histone acetyltransferase GCN5 to the promoter regions of Smad2/3/4, enhancing their transcriptional activation. EMSA confirmed SND1 binds conserved motifs (motifs 1 and 2) in Smad gene promoters. GST pulldown assays showed the Tudor domain of SND1 is responsible for GCN5 recruitment, which increases histone H3K9 acetylation. Loss-of-function of SND1 reduced Smad protein levels and phosphorylation of R-Smads, attenuating TGFβ signaling.","method":"EMSA, GST pulldown, ChIP, co-immunoprecipitation, siRNA knockdown, histone acetylation assay","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1-2 — direct DNA binding by EMSA, domain-specific protein interaction by GST pulldown, histone modification assay, multiple orthogonal methods","pmids":["28263968"],"is_preprint":false},{"year":2019,"finding":"SND1 is identified as an m6A RNA reader. RIP-seq and eCLIP characterised SND1's transcriptome-wide RNA binding profile. The m6A modification of KSHV ORF50 RNA is critical for SND1 binding, which stabilises the ORF50 transcript. SND1 depletion inhibits KSHV early gene expression and is essential for KSHV lytic replication.","method":"RIP-seq, eCLIP, m6A-modified RNA pulldown, siRNA knockdown, viral replication assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — transcriptome-wide binding mapped by eCLIP, m6A-dependency established by modified vs unmodified RNA comparison, functional consequence in viral replication","pmids":["31647415"],"is_preprint":false},{"year":2019,"finding":"SND1 facilitates invasion and migration of cervical cancer cells via Smurf1-mediated ubiquitination and degradation of FOXA2. SND1 knockdown inhibited EMT and lung metastasis in vivo. The pro-metastatic effect of SND1 was dependent on FOXA2 inhibition through Smurf1-mediated degradation.","method":"siRNA knockdown, co-immunoprecipitation, ubiquitination assay, xenograft assay, cell migration/invasion assays","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2-3 — ubiquitination mechanism identified, in vivo validation, mechanistic epistasis established","pmids":["31891682"],"is_preprint":false},{"year":2019,"finding":"PTB-AS (a natural antisense noncoding RNA) promotes PTBP1 mRNA stability by directly binding to its 3'-UTR, and SND1 dramatically increases the binding capacity between PTB-AS and PTBP1 mRNA, masking the miR-9 binding site. This reveals a role for SND1 in facilitating lncRNA-mRNA interactions to stabilize target mRNAs.","method":"RNA immunoprecipitation, siRNA knockdown, mRNA stability assay, luciferase reporter assay","journal":"Molecular therapy","confidence":"Low","confidence_rationale":"Tier 3 — single study, mechanistic role of SND1 in RNA stabilization complex inferred but not directly demonstrated with purified components","pmids":["31253583"],"is_preprint":false},{"year":2020,"finding":"SND1 oncoprotein is identified as an endoplasmic reticulum (ER) membrane-associated protein. The N-terminal peptide of SND1 associates with SEC61A, anchoring SND1 on the ER membrane. The SN domain of SND1 catches and guides nascent MHC-I heavy chain (HC) to ER-associated degradation (ERAD), hindering normal MHC-I assembly. Deletion of SND1 in tumor-bearing mice promotes MHC-I surface presentation and increases CD8+ T cell infiltration.","method":"Subcellular fractionation, co-immunoprecipitation, ERAD assay, domain mapping, in vivo transgenic mouse model (OT-I), flow cytometry","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 — ER localization confirmed by fractionation, interaction with SEC61A and MHC-I HC by co-IP, ERAD mechanism validated, in vivo mouse model with immunological readout","pmids":["32917674"],"is_preprint":false},{"year":2021,"finding":"Pharmacological disruption of the MTDH-SND1 complex with small-molecule compound C26-A6 enhances tumor antigen presentation and synergizes with anti-PD-1 therapy. Mechanistically, the MTDH-SND1 complex reduces antigen presentation by binding to and destabilizing Tap1/2 mRNAs, which encode key components of the antigen-presentation machinery.","method":"Small-molecule compound treatment, RNA immunoprecipitation, mRNA stability assay, FACS (antigen presentation), in vivo tumor models combined with anti-PD-1","journal":"Nature cancer","confidence":"High","confidence_rationale":"Tier 2 — mechanistic RNA binding to Tap1/2 mRNAs demonstrated by RIP, functional consequence confirmed pharmacologically and genetically in vivo","pmids":["35121988"],"is_preprint":false},{"year":2021,"finding":"Genetic ablation of Mtdh in mouse models inhibits breast cancer development through disruption of its interaction with SND1. Small-molecule inhibitors C26-A2 and C26-A6 that specifically disrupt the MTDH-SND1 protein-protein interaction suppressed tumor growth and metastasis and enhanced chemotherapy sensitivity in preclinical TNBC models.","method":"Genetically modified mouse models, small-molecule PPI inhibitor screen, co-immunoprecipitation, in vivo tumor models","journal":"Nature cancer","confidence":"High","confidence_rationale":"Tier 2 — genetic ablation and pharmacological disruption both validate functional requirement of MTDH-SND1 interaction in vivo","pmids":["35121987"],"is_preprint":false},{"year":2022,"finding":"SND1 is localized to mitochondria via an N-terminal mitochondrial targeting sequence (amino acids 1-63), imported through TOM70. In mitochondria, SND1 interacts with PGAM5 and is crucial for PGAM5-DRP1 binding. SND1-mediated mitophagy under stress conditions (FCCP treatment, glucose deprivation) requires both PGAM5 and the SND1 mitochondrial targeting sequence.","method":"Organelle subcellular isolation, mass spectrometry, co-immunoprecipitation (IP-MS), mitophagy assay (FCCP treatment), domain deletion (MTS mutant), in vitro and in vivo tumor growth assays","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 — subcellular localization by fractionation, interaction by IP-MS confirmed, MTS deletion mutant validates mechanism, single lab","pmids":["35433434"],"is_preprint":false},{"year":2023,"finding":"SND1 binds the 5'-end of SARS-CoV-2 negative-sense viral RNA and is required for viral RNA synthesis. SND1-depleted cells form smaller replication organelles and show diminished virus growth kinetics. SND1 directly interacts with the viral RNA-binding protein NSP9 and remodels NSP9 occupancy on viral RNA, altering NSP9's covalent linkage to initiating nucleotides at replication-transcription initiation sites.","method":"Biochemical RNA-protein interaction mapping, iCLIP/eCLIP, co-immunoprecipitation, siRNA depletion, electron microscopy of replication organelles, viral replication kinetics assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical mapping, direct interaction with NSP9 confirmed, depletion phenotype with mechanistic explanation, published in Cell","pmids":["37794589"],"is_preprint":false},{"year":2023,"finding":"SNAI3-AS1 lncRNA competitively binds SND1 and perturbs m6A-dependent recognition of Nrf2 mRNA 3'-UTR by SND1, thereby reducing Nrf2 mRNA stability. SND1 overexpression rescues ferroptosis resistance phenotypes lost upon SNAI3-AS1 overexpression, placing SND1 as an m6A reader that stabilizes Nrf2 mRNA in glioma.","method":"RNA pulldown, RIP, MeRIP (m6A-IP), dual-luciferase reporter assay, gain/loss-of-function rescue experiments, in vitro and in vivo ferroptosis assays","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — m6A-dependent RNA binding confirmed by MeRIP-RIP, rescue experiments establish epistasis, single lab","pmids":["37202791"],"is_preprint":false},{"year":2017,"finding":"TSN (Tudor-SN/SND1)-mediated miRNA decay (TumiD) requires the RNA helicase UPF1 in cellular contexts. UPF1 dissociates miRNAs from their mRNA targets, making AGO2-loaded miRNAs susceptible to TSN-mediated nuclease degradation. Deep miRNA sequencing showed ~50% of candidate TumiD targets are augmented by UPF1, and UPF1-augmented TumiD promotes cancer cell invasion by degrading anti-invasive miRNAs.","method":"In vitro TSN nuclease assay with AGO2-loaded miRNAs, miR-seq (deep sequencing), siRNA knockdown of UPF1, cell invasion assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro nuclease reconstitution, transcriptome-wide miRNA sequencing, loss-of-function with mechanistic and phenotypic readouts","pmids":["28827400"],"is_preprint":false},{"year":2012,"finding":"A chromosomal rearrangement between 7q32 and 7q34 generates an SND1-BRAF fusion protein in c-Met inhibitor-resistant gastric cancer cells. The SND1-BRAF fusion is constitutively active, hyperactivates the downstream MAPK pathway, and confers resistance to c-Met receptor tyrosine kinase inhibition. Combination treatment with a BRAF or MEK inhibitor circumvented resistance.","method":"Chromosomal rearrangement characterization, Western blot (ERK/MEK phosphorylation), ectopic expression, drug resistance assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 — fusion protein identified and functionally characterized with signaling readout and drug sensitivity assay","pmids":["22745804"],"is_preprint":false},{"year":2000,"finding":"The p100/SND1 coactivator protein was identified in endoplasmic reticulum and cytosolic lipid droplets of milk-secreting cells, in addition to its known nuclear localization. Immunofluorescence microscopy confirmed non-nuclear localization in mammary epithelial cells. The abundance of p100 was increased in the lactating state by a post-transcriptional mechanism (without change in mRNA levels), suggesting regulated subcellular distribution.","method":"Subcellular fractionation, immunofluorescence microscopy, Western blot","journal":"Biochimica et biophysica acta","confidence":"Low","confidence_rationale":"Tier 3 — localization identified by fractionation and immunofluorescence, functional consequence not established","pmids":["11099861"],"is_preprint":false},{"year":2015,"finding":"LncRNA-HIT forms a nuclear complex with p100 (SND1) and CBP in limb mesenchyme. ChIRP-seq revealed LncRNA-HIT-p100/CBP complexes associate with multiple loci involved in chondrogenic differentiation. siRNA reduction of p100 significantly decreased expression of LncRNA-HIT-associated chondrogenic loci and impacted H3K27ac, establishing SND1 as a component of a lncRNA-guided epigenetic regulatory complex required for chondrogenesis.","method":"Co-immunoprecipitation (nuclear complex), ChIRP-seq, siRNA knockdown, histone acetylation (H3K27ac) measurement, cartilage nodule formation assay","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide ChIRP-seq, complex confirmed by co-IP, siRNA functional validation with epigenetic and developmental readout","pmids":["26633036"],"is_preprint":false}],"current_model":"SND1 (Tudor-SN/p100 coactivator) is a multifunctional RNA- and protein-binding scaffold that acts as: (1) a transcriptional coactivator bridging sequence-specific activators (STAT6, c-Myb, Smad2/3/4) to RNA polymerase II and the histone acetyltransferase GCN5 via its SN-like and Tudor domains; (2) a spliceosome-associated factor whose TSN domain engages methylated snRNP components (structurally confirmed by crystal structure) to accelerate spliceosome assembly and promote alternative splicing of cancer-relevant exons (e.g., CD44) in concert with SAM68; (3) an m6A RNA reader that stabilizes target mRNAs including viral (KSHV ORF50, SARS-CoV-2 RNA) and cellular (Nrf2, AT1R) transcripts; (4) a component of TSN-mediated miRNA decay (TumiD), working with UPF1 to degrade miRNAs; (5) an ER membrane-associated protein (anchored via SEC61A) that diverts nascent MHC-I heavy chain to ERAD to suppress antigen presentation; (6) a mitochondria-targeted protein (via N-terminal MTS imported through TOM70) that interacts with PGAM5 to promote mitophagy; and (7) an oncogenic interactor of MTDH that stabilizes tumor-initiating cells, promotes metastasis, and suppresses antitumor immunity by destabilizing Tap1/2 mRNAs—an interaction now pharmacologically targetable."},"narrative":{"teleology":[{"year":1998,"claim":"Establishing SND1 as a transcriptional coactivator: SND1 was linked to signal-dependent gene activation when it was shown to form a Pim-1-phosphorylated complex that potentiates c-Myb transcriptional activity downstream of Ras signaling.","evidence":"Yeast two-hybrid, in vitro kinase assay, co-IP, and reporter assays in mammalian cells","pmids":["9809063"],"confidence":"High","gaps":["Phosphorylation sites on SND1 by Pim-1 not mapped","Whether phosphorylation is required for coactivator function was not tested"]},{"year":2002,"claim":"The coactivator mechanism was generalized when SND1's SN-like domain was shown to bridge STAT6 to RNA polymerase II, establishing it as a modular adaptor for cytokine-induced transcription.","evidence":"Reciprocal co-IP, in vitro binding, domain mapping, IL-4-induced Igε reporter assay","pmids":["12234934"],"confidence":"High","gaps":["Structural basis of SN-domain interaction with STAT6 TAD not resolved","Whether other STATs use the same interface was untested"]},{"year":2007,"claim":"SND1 was revealed to have a dual nuclear function — beyond transcription, its Tudor (TSN) domain directly accelerates spliceosome assembly by engaging methylated snRNP components, a mechanism explained at atomic resolution by crystallography.","evidence":"In vitro reconstituted splicing assay with purified SND1/TSN domain; X-ray crystal structure of TSN domain with snRNP peptides","pmids":["17576664","17632523"],"confidence":"High","gaps":["Identity of specific snRNP methylation marks required in vivo not defined","Relative contribution of splicing vs. transcription roles to cellular phenotype unclear"]},{"year":2008,"claim":"SND1 was shown to possess an RISC/AGO2-independent mRNA-stabilizing activity, binding the AT1R 3′-UTR via its SN domains to reduce mRNA decay and enhance translation, broadening its function to post-transcriptional gene regulation.","evidence":"RNA pull-down, mRNA decay assay, overexpression/knockdown, domain deletion mapping","pmids":["18603592"],"confidence":"Medium","gaps":["Transcriptome-wide scope of SND1-mediated mRNA stabilization not yet mapped","Mechanism by which SN domains protect mRNA from decay not defined"]},{"year":2011,"claim":"The discovery of the MTDH–SND1 interaction established SND1 as a key oncogenic effector: the complex promotes lung metastasis and sustains tumor-initiating cells in breast cancer.","evidence":"Mass spectrometry interactome, co-IP, shRNA knockdown, in vivo metastasis assay in mouse models","pmids":["21478147","24981741"],"confidence":"High","gaps":["How MTDH stabilizes SND1 at the molecular level was not resolved at this stage","Cell-type specificity of MTDH-SND1 oncogenic function unexplored"]},{"year":2014,"claim":"The structural basis of the MTDH–SND1 complex was determined at high resolution, revealing a two-tryptophan anchor of MTDH in the SN1/2 groove of SND1 — providing the template for pharmacological disruption.","evidence":"X-ray crystallography, site-directed mutagenesis with functional validation in cancer cells","pmids":["25242325"],"confidence":"High","gaps":["Whether endogenous post-translational modifications modulate the interface was unknown","No small-molecule inhibitors yet existed"]},{"year":2013,"claim":"SND1's splicing function was connected to cancer biology when it was shown to recruit SAM68 and spliceosomal components to CD44 pre-mRNA, promoting inclusion of variable exons that drive prostate cancer cell proliferation and migration.","evidence":"Reciprocal co-IP, RNA immunoprecipitation, alternative splicing RT-PCR, siRNA knockdown with migration/proliferation assays","pmids":["23995791"],"confidence":"Medium","gaps":["Full set of SND1-regulated alternative splicing events in cancer not catalogued","Whether SAM68 is required for all SND1 splicing targets unknown"]},{"year":2015,"claim":"SND1 was placed within the TGFβ signaling cascade: Smad2/3 directly activates SND1 transcription, and SND1 in turn promotes Smurf1-mediated RhoA degradation, connecting SND1 to cytoskeletal remodeling and metastasis.","evidence":"ChIP on SND1 promoter, reporter assay, co-IP, siRNA epistasis, in vivo metastasis model","pmids":["25596283"],"confidence":"High","gaps":["Whether SND1 directly activates Smurf1 transcription or acts post-transcriptionally was not resolved","Generalizability beyond breast cancer metastasis models untested"]},{"year":2017,"claim":"The nuclease activity of SND1 was functionally contextualized: SND1's Tudor domain cooperates with UPF1 to degrade AGO2-loaded miRNAs (TumiD), with ~50% of TumiD targets being UPF1-dependent, linking SND1-mediated miRNA decay to cancer cell invasion.","evidence":"In vitro nuclease reconstitution with AGO2-loaded miRNAs, genome-wide miR-seq, siRNA knockdown, cell invasion assay","pmids":["28827400"],"confidence":"High","gaps":["Structural basis for how UPF1 renders miRNAs accessible to SND1 nuclease activity unresolved","In vivo physiological relevance of TumiD in non-cancer contexts unknown"]},{"year":2017,"claim":"SND1's transcriptional coactivation mechanism was further refined: the Tudor domain recruits GCN5 to Smad promoters, increasing H3K9 acetylation and creating a positive feedback loop within TGFβ signaling.","evidence":"EMSA for direct DNA binding, GST pulldown for Tudor-GCN5 interaction, ChIP for H3K9ac, siRNA knockdown","pmids":["28263968"],"confidence":"High","gaps":["Whether SND1-GCN5 recruitment extends beyond Smad promoters not mapped genome-wide","Structural details of Tudor-GCN5 interface unknown"]},{"year":2019,"claim":"SND1 was identified as an m⁶A RNA reader, establishing a new molecular activity: SND1 preferentially binds m⁶A-modified RNAs including KSHV ORF50 to stabilize them, a function essential for viral lytic replication.","evidence":"RIP-seq, eCLIP, m⁶A-modified vs. unmodified RNA pulldown, siRNA knockdown with viral replication assay","pmids":["31647415"],"confidence":"High","gaps":["Structural basis for m⁶A recognition by SND1 not determined","Whether m⁶A reading uses the same domain as other RNA-binding activities was unclear"]},{"year":2020,"claim":"SND1 was found to suppress antigen presentation from the ER: anchored to the ER membrane via SEC61A, it diverts nascent MHC-I heavy chains to ERAD, and its deletion in tumor-bearing mice restores surface MHC-I and increases CD8⁺ T cell infiltration.","evidence":"Subcellular fractionation, co-IP with SEC61A and MHC-I HC, ERAD assay, in vivo OT-I mouse model, flow cytometry","pmids":["32917674"],"confidence":"High","gaps":["Whether SND1 acts catalytically or as a chaperone in ERAD not distinguished","Relationship between ER-localized SND1 and nuclear SND1 pools not established"]},{"year":2021,"claim":"The MTDH–SND1 complex was shown to suppress antigen presentation through a second, RNA-level mechanism — destabilizing Tap1/2 mRNAs — and small-molecule disruptors of this complex synergized with anti-PD-1 therapy, validating pharmacological targetability.","evidence":"Small-molecule PPI inhibitors (C26-A6), RIP for Tap1/2 mRNAs, mRNA stability assay, FACS, genetic mouse models, combination immunotherapy in vivo","pmids":["35121988","35121987"],"confidence":"High","gaps":["Selectivity and pharmacokinetic profiles of C26 compounds for clinical translation incomplete","Whether Tap1/2 mRNA destabilization requires m⁶A reading function not tested"]},{"year":2022,"claim":"SND1 was localized to mitochondria via an N-terminal targeting sequence imported through TOM70, where it interacts with PGAM5 to facilitate DRP1-dependent mitophagy under stress — adding a mitochondrial dimension to its functions.","evidence":"Mitochondrial fractionation, IP-MS, MTS deletion mutant, FCCP-induced mitophagy assay, in vivo tumor growth","pmids":["35433434"],"confidence":"Medium","gaps":["How the same N-terminal sequence mediates both ER anchoring and mitochondrial import is unresolved","Whether mitochondrial SND1 retains RNA-binding or nuclease activity unknown"]},{"year":2023,"claim":"SND1 was established as a host factor essential for SARS-CoV-2 RNA synthesis: it binds the 5′-end of negative-sense viral RNA, directly interacts with NSP9, and remodels NSP9 occupancy at replication-transcription initiation sites.","evidence":"iCLIP/eCLIP, co-IP with NSP9, siRNA depletion with viral kinetics and EM of replication organelles","pmids":["37794589"],"confidence":"High","gaps":["Whether SND1's m⁶A-reading function contributes to SARS-CoV-2 RNA binding not resolved","Structural basis of SND1-NSP9 interaction unknown"]},{"year":null,"claim":"Major open questions include: how a single protein distributes among nuclear, ER, and mitochondrial pools; the structural basis of m⁶A recognition; and whether the nuclease, m⁶A-reading, and mRNA-stabilizing activities are executed by the same or distinct domain configurations.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unified model for SND1 subcellular partitioning","m⁶A reader domain identity not structurally defined","Relative contributions of SND1's multiple activities to tumorigenesis not dissected genetically in a single system"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[2,5,6,14,16,21,22]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,1,13,26]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[23]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[13]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[13]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[17,18]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,1,2,3,13,26]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[17,25]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4,5,25]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[20]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[25]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,13,26]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[2,8,14,23]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[17,18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[11,15]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[17,12]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[20]}],"complexes":["MTDH-SND1 complex","RISC","TumiD (TSN-UPF1 miRNA decay complex)"],"partners":["MTDH","SAM68","GCN5","UPF1","SEC61A1","PGAM5","STAT6","PIM1"],"other_free_text":[]},"mechanistic_narrative":"SND1 is a multidomain RNA- and protein-binding scaffold that integrates transcriptional coactivation, pre-mRNA splicing, mRNA stability control, and immune evasion across nuclear, cytoplasmic, ER-membrane, and mitochondrial compartments. In the nucleus, SND1 bridges sequence-specific transcription factors (STAT6, c-Myb, Smad2/3/4) to RNA polymerase II and recruits the histone acetyltransferase GCN5 to target promoters, while its Tudor (TSN) domain engages methylated spliceosomal snRNP components to accelerate spliceosome assembly and direct alternative splicing of transcripts such as CD44 in concert with SAM68 [PMID:12234934, PMID:28263968, PMID:17576664, PMID:23995791]. SND1 functions as an N6-methyladenosine (m⁶A) RNA reader that stabilizes both viral (KSHV ORF50, SARS-CoV-2) and cellular (Nrf2, AT1R) transcripts, and as a Tudor-domain nuclease that, together with UPF1, degrades AGO2-loaded miRNAs via TumiD [PMID:31647415, PMID:37794589, PMID:28827400, PMID:18603592]. At the endoplasmic reticulum, SND1 is anchored through SEC61A and diverts nascent MHC-I heavy chains to ERAD, while its complex with MTDH destabilizes Tap1/2 mRNAs, jointly suppressing antigen presentation — a mechanism now pharmacologically targetable with small-molecule inhibitors that synergize with anti-PD-1 immunotherapy [PMID:32917674, PMID:35121988, PMID:35121987]."},"prefetch_data":{"uniprot":{"accession":"Q7KZF4","full_name":"Staphylococcal nuclease domain-containing protein 1","aliases":["100 kDa coactivator","EBNA2 coactivator p100","Tudor domain-containing protein 11","p100 co-activator"],"length_aa":910,"mass_kda":102.0,"function":"Endonuclease that mediates miRNA decay of both protein-free and AGO2-loaded miRNAs (PubMed:18453631, PubMed:28546213). As part of its function in miRNA decay, regulates mRNAs involved in G1-to-S phase transition (PubMed:28546213). Functions as a bridging factor between STAT6 and the basal transcription factor (PubMed:12234934). Plays a role in PIM1 regulation of MYB activity (PubMed:9809063). Functions as a transcriptional coactivator for STAT5 (By similarity) (Microbial infection) Functions as a transcriptional coactivator for the Epstein-Barr virus nuclear antigen 2 (EBNA2) (Microbial infection) Promotes SARS-CoV-2 RNA synthesis by binding to negative-sense RNA and the viral protein nsp9","subcellular_location":"Cytoplasm; Nucleus; Melanosome","url":"https://www.uniprot.org/uniprotkb/Q7KZF4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SND1","classification":"Not 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assay) in a single study\",\n      \"pmids\": [\"9809063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"p100 (SND1) was identified as a coactivator for STAT6 that bridges STAT6 with RNA polymerase II; the interaction is mediated by the TAD domain of STAT6 and the SN-like domain of p100, and p100 enhanced STAT6-mediated transcriptional activation and IL-4-induced Igε gene transcription in human B cells.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding assay, transcriptional reporter assay, mass spectrometry\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reciprocal co-IP, domain mapping, functional transcription assay with orthogonal methods\",\n      \"pmids\": [\"12234934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The TSN domain of p100 (SND1) specifically interacts with components of U5 snRNP and other spliceosomal snRNPs; purified p100 and its isolated TSN domain accelerate spliceosome complex A formation and the A-to-B transition, and enhance the kinetics of the first step of splicing in vitro.\",\n      \"method\": \"Co-immunoprecipitation, in vitro splicing assay with purified TSN domain, dose-response analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro splicing with purified domain, domain-specific interaction mapping\",\n      \"pmids\": [\"17576664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Crystal structure of the p100 TSN domain reveals an interdigitated hook-like structure with a conserved aromatic cage that hooks methyl groups of snRNP proteins, providing the molecular basis for p100's association with the spliceosome.\",\n      \"method\": \"X-ray crystallography, structure-guided functional analysis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mechanistic interpretation validated against known functional data\",\n      \"pmids\": [\"17632523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mass spectrometry-based screen identified SND1 as a MTDH (Metadherin)-interacting protein; the interaction was confirmed by co-immunoprecipitation, and SND1 was shown to promote lung metastasis and resistance to apoptosis in breast cancer models.\",\n      \"method\": \"Mass spectrometry, co-immunoprecipitation, loss-of-function (siRNA), in vivo metastasis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MS discovery confirmed by co-IP, with functional KD phenotype in vivo\",\n      \"pmids\": [\"21478147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"High-resolution crystal structure of the MTDH-SND1 complex revealed an 11-residue MTDH peptide motif occupying an extended groove between SN1 and SN2 domains of SND1, with two MTDH tryptophan residues engaging two defined pockets; mutations at both tryptophan-binding pockets impaired breast cancer-promoting activity.\",\n      \"method\": \"X-ray crystallography, mutagenesis, functional cancer assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis validation of functional interface\",\n      \"pmids\": [\"25242325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MTDH supports mammary tumor cell survival under oncogenic/stress conditions by interacting with and stabilizing SND1; silencing MTDH or SND1 individually, or disrupting their interaction, compromises tumorigenic potential of tumor-initiating cells in vivo.\",\n      \"method\": \"Mouse models (multiple breast cancer subtypes), co-immunoprecipitation, siRNA knockdown, in vivo tumorigenesis assay\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic mouse models combined with co-IP and in vivo functional validation\",\n      \"pmids\": [\"24981741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SND1 functions as an m6A RNA reader through its Tudor domain; RIP-seq and eCLIP defined the SND1 transcriptome-wide binding profile, showing that m6A modification is critical for SND1 binding to KSHV ORF50 RNA, which SND1 stabilizes; SND1 depletion inhibits KSHV lytic replication.\",\n      \"method\": \"RIP-seq, eCLIP, m6A-modified RNA pulldown, SND1 depletion (siRNA), viral replication assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — transcriptome-wide binding profiling plus mechanistic validation of m6A dependence and functional consequence\",\n      \"pmids\": [\"31647415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"p100 (SND1) binds to the AT1R 3'-UTR through its SN-like domains and increases receptor expression by decreasing mRNA decay rate and enhancing translation; this effect is independent of Argonaute2 and RISC.\",\n      \"method\": \"RNA immunoprecipitation, mRNA decay assay, translation assay, siRNA knockdown, deletion mutagenesis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing domain-specific RNA binding and functional consequence on mRNA stability and translation\",\n      \"pmids\": [\"18603592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SND1 interacts with SAM68 in prostate cancer cells (identified by mass spectrometry); SND1 promotes inclusion of CD44 variable exons by recruiting SAM68 and spliceosomal components on CD44 pre-mRNA, and this requires SAM68 and its binding sites on CD44 pre-mRNA. SND1 knockdown reduced PCa cell proliferation and migration.\",\n      \"method\": \"Mass spectrometry, co-immunoprecipitation, splicing reporter assays, RNA immunoprecipitation, siRNA knockdown\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MS-confirmed interaction with mechanistic splicing assays and functional KD phenotype\",\n      \"pmids\": [\"23995791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SND1 acts downstream of TGFβ1/Smad2/3 signaling (Smad complex transcriptionally activates SND1 promoter); SND1 in turn promotes Smurf1 expression, leading to RhoA ubiquitination and degradation, disrupting F-actin organization and increasing breast cancer cell migration and invasion.\",\n      \"method\": \"Chromatin immunoprecipitation, promoter reporter assay, co-immunoprecipitation, ubiquitination assay, migration/invasion assay, in vivo metastasis model\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pathway epistasis established by ChIP, ubiquitination assay, and in vivo metastasis validation\",\n      \"pmids\": [\"25596283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SND1 physically associates with histone acetyltransferase GCN5 and recruits it to the promoters of Smad2/3/4 to enhance their transcription; the Tudor domain of SND1 mediates GCN5 recruitment and increases histone H3K9 acetylation at Smad gene promoters. SND1 also directly recognizes conserved motifs in Smad promoters as shown by EMSA.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown (Tudor domain), EMSA, chromatin immunoprecipitation, histone acetylation assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — domain-specific GST pulldown, EMSA, and ChIP with orthogonal methods\",\n      \"pmids\": [\"28263968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SND1 is an ER membrane-associated protein; its N-terminal peptide associates with SEC61A to anchor on the ER membrane. The SN domain of SND1 catches nascent MHC-I heavy chain and guides it to ER-associated degradation (ERAD), hindering MHC-I assembly and impairing antigen presentation to CD8+ T cells in tumor models.\",\n      \"method\": \"Subcellular fractionation, co-immunoprecipitation, ERAD assay, in vivo tumor model with SND1 deletion, flow cytometry\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment tied to functional consequence, domain mapping, in vivo validation\",\n      \"pmids\": [\"32917674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The MTDH-SND1 complex binds to and destabilizes Tap1/2 mRNAs (encoding antigen-presentation machinery components), reducing tumor antigen presentation and inhibiting T cell infiltration; pharmacological disruption of the complex with compound C26-A6 restored antigen presentation and synergized with anti-PD-1 therapy.\",\n      \"method\": \"RNA immunoprecipitation, mRNA stability assay, small-molecule compound treatment, mouse tumor models, T cell functional assays\",\n      \"journal\": \"Nature cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — RIP-based mechanism with pharmacological disruption and in vivo validation\",\n      \"pmids\": [\"35121988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Genetic ablation of Mtdh inhibits breast cancer development specifically through disrupting its interaction with SND1; small-molecule compounds C26-A2 and C26-A6 that disrupt the MTDH-SND1 protein-protein interaction suppressed tumor growth and metastasis and enhanced chemotherapy sensitivity in TNBC preclinical models.\",\n      \"method\": \"Genetically modified mouse models, small-molecule PPI inhibitor screen, in vitro and in vivo tumor assays\",\n      \"journal\": \"Nature cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic mouse model epistasis plus pharmacological PPI disruption with in vivo validation\",\n      \"pmids\": [\"35121987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SND1 binds the 5' end of SARS-CoV-2 negative-sense viral RNA and is required for viral RNA synthesis; SND1-depleted cells form smaller replication organelles and show diminished virus growth. SND1 interacts directly with viral NSP9 and remodels NSP9 occupancy and covalent linkage to initiating nucleotides at replication-transcription initiation sites.\",\n      \"method\": \"Biochemical RNA-protein pulldown, eCLIP, co-immunoprecipitation, SND1 depletion, cryo-EM/organelle imaging, viral replication assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multi-method study with direct protein-RNA interaction mapping, protein-protein interaction, and functional viral replication readout\",\n      \"pmids\": [\"37794589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"p100 (SND1) was identified by RNA affinity capture and mass spectrometry as a host protein binding the dengue virus 3' UTR (specifically the A4 stem-loop region); p100 knockdown reduced viral RNA levels and viral protein expression in DENV-infected cells, implicating p100 in DENV replication.\",\n      \"method\": \"RNA affinity capture, mass spectrometry, RNA immunoprecipitation, confocal immunofluorescence, siRNA knockdown, luciferase reporter assay\",\n      \"journal\": \"The Journal of general virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MS discovery confirmed by RIP and functional KD with viral replication readout\",\n      \"pmids\": [\"21148275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SND1 interacts with monoglyceride lipase (MGLL) identified by yeast two-hybrid; co-immunoprecipitation confirmed the interaction. SND1-MGLL interaction results in ubiquitination and proteasomal degradation of MGLL, and forced MGLL overexpression in HCC cells inhibited Akt activation and cell proliferation.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, ubiquitination assay, proteasome inhibitor experiment, cell proliferation and xenograft assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Y2H confirmed by co-IP plus ubiquitination mechanism and in vivo functional validation\",\n      \"pmids\": [\"26997225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"UPF1 helicase promotes TSN (SND1)-mediated miRNA decay (TumiD); UPF1 dissociates AGO2-loaded miRNAs from their mRNA targets, making miRNAs susceptible to cleavage by the nuclease TSN. TSN-mediated degradation of miRNAs in vitro does not require UPF1, but cellular TumiD requires UPF1.\",\n      \"method\": \"In vitro nuclease assay, miRNA-seq, siRNA knockdown, invasion assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution distinguishing UPF1-dependent vs -independent steps, plus genome-wide miRNA-seq validation\",\n      \"pmids\": [\"28827400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The p100 coactivator (SND1) protein is present in endoplasmic reticulum and cytosolic lipid droplets of milk-secreting mammary epithelial cells, as shown by fractionation and immunofluorescence microscopy, indicating a non-nuclear subcellular localization in lipid-metabolizing cells.\",\n      \"method\": \"Subcellular fractionation, immunofluorescence microscopy, partial tryptic peptide sequencing\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — direct localization by fractionation and microscopy, but functional consequence not fully defined\",\n      \"pmids\": [\"11099861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SND1 (SND p102) co-fractionates with ER and Golgi markers in hepatocytes and is additionally detected in lipid droplets under steatogenic conditions, with confocal microscopy confirming translocation to low-density lipid droplets in oleate-treated HepG2 cells.\",\n      \"method\": \"Sucrose gradient fractionation, confocal microscopy, organelle marker co-localization\",\n      \"journal\": \"Journal of physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — localization by fractionation and microscopy, functional consequence of lipid droplet association not mechanistically resolved\",\n      \"pmids\": [\"20414760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SND1 overexpression in rat intestinal epithelial cells caused loss of contact inhibition, promoted cell growth, altered E-cadherin distribution from cell membrane to cytoplasm, and coincidentally downregulated APC protein without changing APC mRNA levels, suggesting SND1 acts as a component of RISC to post-transcriptionally regulate APC.\",\n      \"method\": \"Stable overexpression, cell growth assay, immunofluorescence, Western blot, RT-PCR\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — gain-of-function with defined cellular phenotype but indirect mechanistic link to RISC\",\n      \"pmids\": [\"17909068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A chromosomal rearrangement between 7q32 and 7q34 produces a constitutively active SND1-BRAF fusion protein; in resistant GTL16 gastric cancer cells, this fusion hyperactivates the MAPK pathway (MEK/ERK), conferring resistance to c-Met inhibition. Combination with a RAF or MEK inhibitor blocked ERK activation and circumvented resistance.\",\n      \"method\": \"DNA sequencing, genomic characterization, ERK phosphorylation assay, drug combination experiments\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — genomic characterization with biochemical pathway validation, but purely fusion-protein context\",\n      \"pmids\": [\"22745804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LncRNA-HIT forms a complex with p100 (SND1) and CBP in the nucleus; ChIRP-seq revealed genome-wide LncRNA-HIT–p100/CBP complex occupancy at chondrogenic gene loci; siRNA-mediated reduction in p100 decreased expression of LncRNA-HIT-associated loci and impaired cartilage nodule formation.\",\n      \"method\": \"ChIRP-seq, co-immunoprecipitation, siRNA knockdown, in vitro chondrogenesis assay\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide ChIRP-seq with functional KD phenotype, but single lab\",\n      \"pmids\": [\"26633036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SND1 is localized to mitochondria via an N-terminal mitochondrial targeting sequence (aa 1–63) imported through TOM70; mitochondrial SND1 interacts with PGAM5 (identified by IP-MS) and is required for PGAM5-DRP1 binding, promoting mitophagy and liver cancer cell proliferation in vitro and in vivo.\",\n      \"method\": \"Organelle subcellular isolation, mass spectrometry (IP-MS), co-immunoprecipitation, mitochondrial targeting sequence deletion, in vivo xenograft\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with domain mapping plus IP-MS and functional consequence, but single lab\",\n      \"pmids\": [\"35433434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SNAI3-AS1 lncRNA competitively binds to SND1 and perturbs SND1's m6A-dependent recognition of Nrf2 mRNA 3'UTR, thereby reducing Nrf2 mRNA stability and promoting ferroptosis in glioma; SND1 overexpression rescued the ferroptotic phenotype caused by SNAI3-AS1.\",\n      \"method\": \"RNA pulldown, RIP, MeRIP (m6A-IP), dual-luciferase reporter, gain/loss-of-function experiments, in vivo tumor model\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple binding assays with functional rescue, but single lab\",\n      \"pmids\": [\"37202791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SND1 (Tudor-SN) promotes stabilization of PTBP1 mRNA in glioma cells by dramatically increasing the binding capacity between the lncRNA PTB-AS and PTBP1 mRNA; mechanistically, PTB-AS masks the miR-9 binding site in PTBP1 3'UTR and SND1 facilitates this RNA-RNA interaction to maintain PTBP1 levels.\",\n      \"method\": \"RNA immunoprecipitation, RNA pulldown, co-IP, in vivo tumor assay\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — RIP and RNA pulldown supporting mechanistic model, but complex three-way interaction requires further dissection\",\n      \"pmids\": [\"31253583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SND1 promotes expression of lncRNA UCA1 through MYB transcription factor to protect hepatocellular carcinoma cells from apoptosis; SND1 knockdown enhanced 5-Fu-induced apoptosis, and this was rescued by UCA1 overexpression.\",\n      \"method\": \"siRNA knockdown, lentiviral shRNA, apoptosis assay, gene expression analysis, rescue experiment\",\n      \"journal\": \"RNA biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — loss-of-function with phenotypic rescue but no direct biochemical mechanism for SND1-UCA1 regulation established\",\n      \"pmids\": [\"30321081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SND1 promotes cervical cancer invasion and migration via Smurf1-mediated ubiquitination and degradation of FOXA2; SND1 knockdown enhanced FOXA2 expression and inhibited EMT.\",\n      \"method\": \"siRNA knockdown, ubiquitination assay, in vivo lung metastasis model, invasion assay\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — indirect mechanistic link through Smurf1 inferred rather than directly demonstrated for SND1\",\n      \"pmids\": [\"31891682\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SND1 (Tudor-SN/p100) is a multifunctional scaffold protein whose Tudor-SN (TSN) domain reads m6A-modified RNA and hooks methylated snRNP proteins via an aromatic cage, promoting spliceosome assembly; its SN-like domains serve as a transcriptional coactivator bridging STAT6 (and other transcription factors) to RNA Pol II; it regulates mRNA stability and translation by binding 3'-UTRs; it acts as a nuclease in TSN-mediated miRNA decay facilitated by UPF1; it interacts with MTDH through a defined SN1/2 groove to sustain tumor-initiating cell survival and suppress antigen presentation by destabilizing Tap1/2 mRNAs; it is imported into mitochondria via a TOM70-dependent MTS to promote PGAM5-DRP1-dependent mitophagy; and it associates with the ER membrane via SEC61A to redirect nascent MHC-I heavy chains to ERAD, enabling immune evasion in tumors.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper and extract discoveries only from KEEP papers.\n\n**Classification notes:**\n- Papers [1]-[22] (corpus) with NF-κB2/p100, Arabidopsis SND1 (plant NAC domain TF), p100 catenin, HHV-6 p100, visual evoked potential P100, 2',5'-oligoadenylate synthetase p100, complement protease P100, Xenopus P100 (Pat1 orthologue), TSN (Translin, not SND1) → EXCLUDE (alias collisions)\n- Papers about human SND1 (staphylococcal nuclease domain-containing 1, also called Tudor-SN, TSN, p100 coactivator) → KEEP\n- Papers [2],[3],[7],[22] (Arabidopsis SND1 = NAC domain TF) → EXCLUDE\n- Additional curated papers are mostly large proteomics datasets with SND1 as one of many proteins → include only if they describe specific mechanistic findings about SND1\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"Pim-1 kinase was found to interact with p100 (SND1) via yeast two-hybrid screen; Pim-1 phosphorylated p100 in vitro, formed a stable complex with p100 in animal cells, and functioned downstream of Ras to stimulate c-Myb transcriptional activity in a p100-dependent manner, establishing p100/SND1 as a transcriptional coactivator linking cytokine signaling to c-Myb activity.\",\n      \"method\": \"Yeast two-hybrid screen, in vitro phosphorylation assay, co-immunoprecipitation, transactivation assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Y2H, in vitro kinase assay, co-IP, transcriptional reporter) in single study\",\n      \"pmids\": [\"9809063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"p100/SND1 was identified as a coactivator for STAT6 that bridges STAT6 with RNA polymerase II. The interaction was mediated by the TAD domain of STAT6 and the SN-like domain of p100. p100 enhanced STAT6-mediated transcriptional activation and IL-4-induced Igε gene transcription, and associated with the large subunit of RNA polymerase II.\",\n      \"method\": \"Co-immunoprecipitation, in vitro interaction assay, reporter gene assay, domain mapping\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus in vitro binding, domain mapping, and functional reporter assay\",\n      \"pmids\": [\"12234934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The TSN domain of p100/SND1 specifically interacts with components of the U5 snRNP and other spliceosomal snRNPs. Purified p100 and its isolated TSN domain accelerated spliceosome complex A formation and the A-to-B transition in vitro, and enhanced the kinetics of the first splicing step in a dose-dependent manner, revealing a dual role in transcription and pre-mRNA splicing.\",\n      \"method\": \"Co-immunoprecipitation, in vitro splicing assay, domain-specific pull-down\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstituted splicing assay with purified protein, domain-specific functional dissection\",\n      \"pmids\": [\"17576664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Crystal structure of the p100/SND1 TSN domain was determined, revealing an interdigitated hook-like structure with a conserved aromatic cage that hooks methyl groups of snRNP proteins, providing structural explanation for SND1's roles in transcription and spliceosome anchoring.\",\n      \"method\": \"X-ray crystallography, structural analysis of Tudor-SN domain with snRNP peptides\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with functional validation\",\n      \"pmids\": [\"17632523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SND1 was identified as a component of the RNA-induced silencing complex (RISC) and was shown to be up-regulated in human colon cancers. Overexpression of SND1 in intestinal epithelial cells caused loss of contact inhibition, promoted cell growth, altered E-cadherin distribution, and down-regulated APC protein (without altering APC mRNA), implicating SND1-mediated post-transcriptional regulation in colon carcinogenesis.\",\n      \"method\": \"Stable overexpression, cell proliferation assay, immunofluorescence, Western blot, immunohistochemistry\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — overexpression with defined cellular phenotype and molecular readout (APC protein loss without mRNA change), single lab\",\n      \"pmids\": [\"17909068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"p100/SND1 was found to bind the angiotensin II type 1 receptor (AT1R) 3'-UTR via its SN-like domains, increasing AT1R expression by decreasing mRNA decay rate and enhancing translation. This effect was independent of Argonaute2/RISC, revealing a novel mRNA-stabilizing function of SND1.\",\n      \"method\": \"RNA pull-down, p100 silencing, overexpression, mRNA decay assay, deletion mapping of binding site\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNA binding mapped to specific domain, functional consequence on mRNA stability and translation, RISC-independent mechanism demonstrated\",\n      \"pmids\": [\"18603592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Cellular p100/SND1 was identified as a host factor that binds the dengue virus 3'-UTR (specifically the A4 stem-loop region). p100 knockdown reduced viral RNA levels and viral protein expression, and decreased expression of a luciferase-3'UTR(DENV) reporter in an A4-dependent manner, demonstrating that SND1 is required for normal dengue virus replication.\",\n      \"method\": \"RNA affinity capture, mass spectrometry, RNA immunoprecipitation, confocal immunofluorescence, siRNA knockdown, luciferase reporter assay\",\n      \"journal\": \"The Journal of general virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods confirming RNA binding and functional requirement in viral replication\",\n      \"pmids\": [\"21148275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SND1 was identified as a MTDH (Metadherin)-interacting protein by mass spectrometry-based screen. SND1 strongly promotes lung metastasis in breast cancer models and promotes resistance to apoptosis. Silencing SND1 reduced metastatic potential and regulated expression of genes associated with metastasis and chemoresistance.\",\n      \"method\": \"Mass spectrometry interactome screen, co-immunoprecipitation, shRNA knockdown, in vivo metastasis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS-based interaction confirmed by co-IP, loss-of-function with in vivo phenotype\",\n      \"pmids\": [\"21478147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SND1 was found to interact with SAM68 in prostate cancer cells. SND1 upregulation synergizes with SAM68 to promote inclusion of CD44 variable exons. SND1 promotes inclusion of CD44 variable exons by recruiting SAM68 and spliceosomal components to CD44 pre-mRNA. Knockdown of SND1 reduced proliferation and migration of prostate cancer cells.\",\n      \"method\": \"Mass spectrometry, co-immunoprecipitation, RNA immunoprecipitation, siRNA knockdown, alternative splicing analysis, cell migration/proliferation assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, RIP, functional splicing analysis, and loss-of-function phenotype\",\n      \"pmids\": [\"23995791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"High-resolution crystal structure of the MTDH-SND1 complex was determined, revealing that an 11-residue MTDH peptide motif occupies an extended groove between SND1's SN1/2 domains, with two MTDH tryptophan residues nestled into two pockets in SND1. Mutations at both tryptophan-binding pockets impaired MTDH-SND1 interactions and their roles in breast cancer, and also impaired SND1 stability under stress.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, co-immunoprecipitation, cancer cell functional assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with mutagenesis validation and functional phenotype\",\n      \"pmids\": [\"25242325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MTDH-SND1 interaction is crucial for expansion and activity of tumor-initiating cells (TICs) in mammary tumors. Mechanistically, MTDH supports survival of mammary epithelial cells under oncogenic/stress conditions by interacting with and stabilizing SND1. Silencing MTDH or SND1 individually, or disrupting their interaction, compromised tumorigenic potential of TICs in vivo.\",\n      \"method\": \"Mouse mammary tumor models, genetic knockdown, co-immunoprecipitation, tumor-initiating cell assays in vivo\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mouse models, genetic ablation with defined mechanistic readout, in vivo validation\",\n      \"pmids\": [\"24981741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SND1 acts downstream of TGFβ1 and upstream of Smurf1 to promote breast cancer metastasis. TGFβ1/Smad2/Smad3 complex transcriptionally activates SND1 via Smad recognition domains (RD motifs) in the SND1 promoter. SND1 promotes Smurf1 expression, leading to RhoA ubiquitination and degradation, disrupting F-actin organization, reducing cell adhesion, and increasing cell migration and invasion.\",\n      \"method\": \"Promoter analysis, ChIP, reporter assay, co-immunoprecipitation, siRNA knockdown, cell migration/invasion assays, in vivo metastasis model\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established by pathway analysis with multiple orthogonal methods including ChIP, co-IP, and in vivo model\",\n      \"pmids\": [\"25596283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SND1 promotes hepatocarcinogenesis by interacting with and inducing ubiquitination and proteasomal degradation of monoglyceride lipase (MGLL), a tumor suppressor. MGLL overexpression inhibited HCC cell proliferation and tumor growth, and inhibited Akt activation independently of MGLL's enzymatic activity.\",\n      \"method\": \"Yeast two-hybrid assay, co-immunoprecipitation, ubiquitination assay, cell proliferation assay, in vivo xenograft assay, IHC of tissue microarray\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Y2H confirmed by co-IP, ubiquitination mechanism established, in vivo functional validation\",\n      \"pmids\": [\"26997225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SND1 physically associates with and recruits the histone acetyltransferase GCN5 to the promoter regions of Smad2/3/4, enhancing their transcriptional activation. EMSA confirmed SND1 binds conserved motifs (motifs 1 and 2) in Smad gene promoters. GST pulldown assays showed the Tudor domain of SND1 is responsible for GCN5 recruitment, which increases histone H3K9 acetylation. Loss-of-function of SND1 reduced Smad protein levels and phosphorylation of R-Smads, attenuating TGFβ signaling.\",\n      \"method\": \"EMSA, GST pulldown, ChIP, co-immunoprecipitation, siRNA knockdown, histone acetylation assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct DNA binding by EMSA, domain-specific protein interaction by GST pulldown, histone modification assay, multiple orthogonal methods\",\n      \"pmids\": [\"28263968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SND1 is identified as an m6A RNA reader. RIP-seq and eCLIP characterised SND1's transcriptome-wide RNA binding profile. The m6A modification of KSHV ORF50 RNA is critical for SND1 binding, which stabilises the ORF50 transcript. SND1 depletion inhibits KSHV early gene expression and is essential for KSHV lytic replication.\",\n      \"method\": \"RIP-seq, eCLIP, m6A-modified RNA pulldown, siRNA knockdown, viral replication assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — transcriptome-wide binding mapped by eCLIP, m6A-dependency established by modified vs unmodified RNA comparison, functional consequence in viral replication\",\n      \"pmids\": [\"31647415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SND1 facilitates invasion and migration of cervical cancer cells via Smurf1-mediated ubiquitination and degradation of FOXA2. SND1 knockdown inhibited EMT and lung metastasis in vivo. The pro-metastatic effect of SND1 was dependent on FOXA2 inhibition through Smurf1-mediated degradation.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, ubiquitination assay, xenograft assay, cell migration/invasion assays\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — ubiquitination mechanism identified, in vivo validation, mechanistic epistasis established\",\n      \"pmids\": [\"31891682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PTB-AS (a natural antisense noncoding RNA) promotes PTBP1 mRNA stability by directly binding to its 3'-UTR, and SND1 dramatically increases the binding capacity between PTB-AS and PTBP1 mRNA, masking the miR-9 binding site. This reveals a role for SND1 in facilitating lncRNA-mRNA interactions to stabilize target mRNAs.\",\n      \"method\": \"RNA immunoprecipitation, siRNA knockdown, mRNA stability assay, luciferase reporter assay\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single study, mechanistic role of SND1 in RNA stabilization complex inferred but not directly demonstrated with purified components\",\n      \"pmids\": [\"31253583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SND1 oncoprotein is identified as an endoplasmic reticulum (ER) membrane-associated protein. The N-terminal peptide of SND1 associates with SEC61A, anchoring SND1 on the ER membrane. The SN domain of SND1 catches and guides nascent MHC-I heavy chain (HC) to ER-associated degradation (ERAD), hindering normal MHC-I assembly. Deletion of SND1 in tumor-bearing mice promotes MHC-I surface presentation and increases CD8+ T cell infiltration.\",\n      \"method\": \"Subcellular fractionation, co-immunoprecipitation, ERAD assay, domain mapping, in vivo transgenic mouse model (OT-I), flow cytometry\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ER localization confirmed by fractionation, interaction with SEC61A and MHC-I HC by co-IP, ERAD mechanism validated, in vivo mouse model with immunological readout\",\n      \"pmids\": [\"32917674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Pharmacological disruption of the MTDH-SND1 complex with small-molecule compound C26-A6 enhances tumor antigen presentation and synergizes with anti-PD-1 therapy. Mechanistically, the MTDH-SND1 complex reduces antigen presentation by binding to and destabilizing Tap1/2 mRNAs, which encode key components of the antigen-presentation machinery.\",\n      \"method\": \"Small-molecule compound treatment, RNA immunoprecipitation, mRNA stability assay, FACS (antigen presentation), in vivo tumor models combined with anti-PD-1\",\n      \"journal\": \"Nature cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic RNA binding to Tap1/2 mRNAs demonstrated by RIP, functional consequence confirmed pharmacologically and genetically in vivo\",\n      \"pmids\": [\"35121988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Genetic ablation of Mtdh in mouse models inhibits breast cancer development through disruption of its interaction with SND1. Small-molecule inhibitors C26-A2 and C26-A6 that specifically disrupt the MTDH-SND1 protein-protein interaction suppressed tumor growth and metastasis and enhanced chemotherapy sensitivity in preclinical TNBC models.\",\n      \"method\": \"Genetically modified mouse models, small-molecule PPI inhibitor screen, co-immunoprecipitation, in vivo tumor models\",\n      \"journal\": \"Nature cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic ablation and pharmacological disruption both validate functional requirement of MTDH-SND1 interaction in vivo\",\n      \"pmids\": [\"35121987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SND1 is localized to mitochondria via an N-terminal mitochondrial targeting sequence (amino acids 1-63), imported through TOM70. In mitochondria, SND1 interacts with PGAM5 and is crucial for PGAM5-DRP1 binding. SND1-mediated mitophagy under stress conditions (FCCP treatment, glucose deprivation) requires both PGAM5 and the SND1 mitochondrial targeting sequence.\",\n      \"method\": \"Organelle subcellular isolation, mass spectrometry, co-immunoprecipitation (IP-MS), mitophagy assay (FCCP treatment), domain deletion (MTS mutant), in vitro and in vivo tumor growth assays\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — subcellular localization by fractionation, interaction by IP-MS confirmed, MTS deletion mutant validates mechanism, single lab\",\n      \"pmids\": [\"35433434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SND1 binds the 5'-end of SARS-CoV-2 negative-sense viral RNA and is required for viral RNA synthesis. SND1-depleted cells form smaller replication organelles and show diminished virus growth kinetics. SND1 directly interacts with the viral RNA-binding protein NSP9 and remodels NSP9 occupancy on viral RNA, altering NSP9's covalent linkage to initiating nucleotides at replication-transcription initiation sites.\",\n      \"method\": \"Biochemical RNA-protein interaction mapping, iCLIP/eCLIP, co-immunoprecipitation, siRNA depletion, electron microscopy of replication organelles, viral replication kinetics assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical mapping, direct interaction with NSP9 confirmed, depletion phenotype with mechanistic explanation, published in Cell\",\n      \"pmids\": [\"37794589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SNAI3-AS1 lncRNA competitively binds SND1 and perturbs m6A-dependent recognition of Nrf2 mRNA 3'-UTR by SND1, thereby reducing Nrf2 mRNA stability. SND1 overexpression rescues ferroptosis resistance phenotypes lost upon SNAI3-AS1 overexpression, placing SND1 as an m6A reader that stabilizes Nrf2 mRNA in glioma.\",\n      \"method\": \"RNA pulldown, RIP, MeRIP (m6A-IP), dual-luciferase reporter assay, gain/loss-of-function rescue experiments, in vitro and in vivo ferroptosis assays\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — m6A-dependent RNA binding confirmed by MeRIP-RIP, rescue experiments establish epistasis, single lab\",\n      \"pmids\": [\"37202791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"TSN (Tudor-SN/SND1)-mediated miRNA decay (TumiD) requires the RNA helicase UPF1 in cellular contexts. UPF1 dissociates miRNAs from their mRNA targets, making AGO2-loaded miRNAs susceptible to TSN-mediated nuclease degradation. Deep miRNA sequencing showed ~50% of candidate TumiD targets are augmented by UPF1, and UPF1-augmented TumiD promotes cancer cell invasion by degrading anti-invasive miRNAs.\",\n      \"method\": \"In vitro TSN nuclease assay with AGO2-loaded miRNAs, miR-seq (deep sequencing), siRNA knockdown of UPF1, cell invasion assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro nuclease reconstitution, transcriptome-wide miRNA sequencing, loss-of-function with mechanistic and phenotypic readouts\",\n      \"pmids\": [\"28827400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A chromosomal rearrangement between 7q32 and 7q34 generates an SND1-BRAF fusion protein in c-Met inhibitor-resistant gastric cancer cells. The SND1-BRAF fusion is constitutively active, hyperactivates the downstream MAPK pathway, and confers resistance to c-Met receptor tyrosine kinase inhibition. Combination treatment with a BRAF or MEK inhibitor circumvented resistance.\",\n      \"method\": \"Chromosomal rearrangement characterization, Western blot (ERK/MEK phosphorylation), ectopic expression, drug resistance assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — fusion protein identified and functionally characterized with signaling readout and drug sensitivity assay\",\n      \"pmids\": [\"22745804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The p100/SND1 coactivator protein was identified in endoplasmic reticulum and cytosolic lipid droplets of milk-secreting cells, in addition to its known nuclear localization. Immunofluorescence microscopy confirmed non-nuclear localization in mammary epithelial cells. The abundance of p100 was increased in the lactating state by a post-transcriptional mechanism (without change in mRNA levels), suggesting regulated subcellular distribution.\",\n      \"method\": \"Subcellular fractionation, immunofluorescence microscopy, Western blot\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — localization identified by fractionation and immunofluorescence, functional consequence not established\",\n      \"pmids\": [\"11099861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LncRNA-HIT forms a nuclear complex with p100 (SND1) and CBP in limb mesenchyme. ChIRP-seq revealed LncRNA-HIT-p100/CBP complexes associate with multiple loci involved in chondrogenic differentiation. siRNA reduction of p100 significantly decreased expression of LncRNA-HIT-associated chondrogenic loci and impacted H3K27ac, establishing SND1 as a component of a lncRNA-guided epigenetic regulatory complex required for chondrogenesis.\",\n      \"method\": \"Co-immunoprecipitation (nuclear complex), ChIRP-seq, siRNA knockdown, histone acetylation (H3K27ac) measurement, cartilage nodule formation assay\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide ChIRP-seq, complex confirmed by co-IP, siRNA functional validation with epigenetic and developmental readout\",\n      \"pmids\": [\"26633036\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SND1 (Tudor-SN/p100 coactivator) is a multifunctional RNA- and protein-binding scaffold that acts as: (1) a transcriptional coactivator bridging sequence-specific activators (STAT6, c-Myb, Smad2/3/4) to RNA polymerase II and the histone acetyltransferase GCN5 via its SN-like and Tudor domains; (2) a spliceosome-associated factor whose TSN domain engages methylated snRNP components (structurally confirmed by crystal structure) to accelerate spliceosome assembly and promote alternative splicing of cancer-relevant exons (e.g., CD44) in concert with SAM68; (3) an m6A RNA reader that stabilizes target mRNAs including viral (KSHV ORF50, SARS-CoV-2 RNA) and cellular (Nrf2, AT1R) transcripts; (4) a component of TSN-mediated miRNA decay (TumiD), working with UPF1 to degrade miRNAs; (5) an ER membrane-associated protein (anchored via SEC61A) that diverts nascent MHC-I heavy chain to ERAD to suppress antigen presentation; (6) a mitochondria-targeted protein (via N-terminal MTS imported through TOM70) that interacts with PGAM5 to promote mitophagy; and (7) an oncogenic interactor of MTDH that stabilizes tumor-initiating cells, promotes metastasis, and suppresses antitumor immunity by destabilizing Tap1/2 mRNAs—an interaction now pharmacologically targetable.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SND1 (Tudor-SN/p100) is a multifunctional scaffold protein that couples RNA metabolism, transcriptional coactivation, and protein quality control to regulate gene expression, splicing, and immune evasion. Its C-terminal Tudor domain contains an aromatic cage that reads methylated snRNP proteins to accelerate spliceosome assembly and recognizes m6A-modified RNA to regulate mRNA stability, while also recruiting the histone acetyltransferase GCN5 to activate target gene promoters [PMID:17576664, PMID:17632523, PMID:31647415, PMID:28263968]. The four N-terminal SN-like domains bridge transcription factors (STAT6, c-Myb) to RNA Pol II and mediate direct RNA binding at 3′-UTRs to control mRNA decay and translation, and SND1 also functions as a nuclease in UPF1-facilitated miRNA degradation (TumiD) [PMID:12234934, PMID:18603592, PMID:28827400]. Through its SN1/SN2 groove, SND1 forms a structurally defined complex with MTDH that sustains tumor-initiating cell survival, destabilizes Tap1/2 mRNAs encoding antigen-presentation machinery, and directs nascent MHC-I heavy chains to SEC61A-dependent ERAD, establishing SND1 as a central mediator of tumor immune evasion targetable by small-molecule PPI inhibitors [PMID:25242325, PMID:35121988, PMID:32917674, PMID:35121987].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"SND1 was first placed in signal-dependent transcription when Pim-1 kinase was shown to phosphorylate and complex with p100 to stimulate c-Myb transcriptional activity downstream of Ras, establishing SND1 as a transcriptional coactivator.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro kinase assay, co-IP, and reporter assay in mammalian cells\",\n      \"pmids\": [\"9809063\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation sites on SND1 not mapped\", \"Whether Pim-1-dependent phosphorylation is required for all SND1 coactivator functions was untested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The transcriptional coactivator mechanism was generalized beyond c-Myb when SND1's SN domains were shown to bridge STAT6 to RNA Pol II, enhancing IL-4-induced Igε transcription, revealing domain-specific scaffolding as the basis of its coactivator function.\",\n      \"evidence\": \"Reciprocal co-IP, in vitro binding, transcriptional reporter, and mass spectrometry in human B cells\",\n      \"pmids\": [\"12234934\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SND1 acts on additional STAT family members was unknown\", \"Post-translational modifications regulating the STAT6–SND1 interface were not explored\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"A second major function emerged when the Tudor-SN domain was shown to interact with spliceosomal snRNPs and accelerate spliceosome complex formation in vitro, while crystallography revealed an aromatic cage that hooks methylated arginine residues on snRNP proteins, providing the structural basis for splicing promotion.\",\n      \"evidence\": \"Co-IP with snRNP components, reconstituted in vitro splicing, X-ray crystallography of TSN domain\",\n      \"pmids\": [\"17576664\", \"17632523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of specific methylated residues on snRNP targets not resolved\", \"In vivo splicing targets not defined genome-wide\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"SND1 was shown to regulate mRNA fate post-transcriptionally by binding 3′-UTRs through its SN domains, stabilizing AT1R mRNA and enhancing its translation independently of AGO2/RISC, extending SND1's role from transcription and splicing to mRNA stability control.\",\n      \"evidence\": \"RIP, mRNA decay assay, translation assay, domain deletion mutagenesis\",\n      \"pmids\": [\"18603592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Breadth of mRNA targets regulated via 3′-UTR binding was not determined\", \"Structural basis of SN-domain RNA recognition was not resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Subcellular localization studies revealed SND1 associates with ER, Golgi, and lipid droplets in hepatocytes and mammary epithelial cells, indicating that a substantial fraction of SND1 operates outside the nucleus.\",\n      \"evidence\": \"Sucrose gradient fractionation, immunofluorescence, and confocal microscopy in HepG2 and mammary cells\",\n      \"pmids\": [\"11099861\", \"20414760\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of lipid-droplet localization was not mechanistically resolved\", \"Whether ER vs. lipid-droplet pools serve distinct functions was unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"A cancer-relevant protein partner was identified when mass spectrometry revealed MTDH as a direct SND1-interacting protein, and loss-of-function experiments linked this complex to lung metastasis and apoptosis resistance, opening the MTDH–SND1 axis in oncology.\",\n      \"evidence\": \"MS-based screen, co-IP, siRNA knockdown, in vivo metastasis assay in breast cancer models\",\n      \"pmids\": [\"21478147\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of MTDH–SND1 interaction was not yet known\", \"Downstream effectors of the complex were undefined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The MTDH–SND1 interface was resolved at atomic resolution, revealing two tryptophan-binding pockets in the SN1/SN2 groove, and genetic studies showed that MTDH stabilizes SND1 to sustain tumor-initiating cell survival, validating the complex as a druggable target.\",\n      \"evidence\": \"X-ray crystallography of MTDH–SND1 complex, mutagenesis, multiple mouse breast cancer models\",\n      \"pmids\": [\"25242325\", \"24981741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Small-molecule inhibitors of the interface were not yet available\", \"Downstream transcriptomic changes driven by the complex were not comprehensively mapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"SND1's Tudor domain was found to recruit GCN5 to Smad2/3/4 promoters, increasing H3K9 acetylation and feeding back into TGFβ signaling, while UPF1 was shown to facilitate TSN-mediated miRNA decay (TumiD), establishing SND1 as an endoribonuclease for miRNAs.\",\n      \"evidence\": \"GST pulldown, ChIP, EMSA for GCN5 recruitment; in vitro nuclease assay and miRNA-seq for TumiD\",\n      \"pmids\": [\"28263968\", \"28827400\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Selectivity of miRNA substrates for TumiD was not fully explained\", \"Whether GCN5 recruitment and nuclease activity occur simultaneously or are context-dependent was unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"SND1 was established as an m6A RNA reader: its Tudor domain binds m6A-modified viral and cellular RNAs to control their stability, as demonstrated for KSHV ORF50 RNA, adding epitranscriptomic sensing to SND1's functional repertoire.\",\n      \"evidence\": \"RIP-seq, eCLIP, m6A-modified RNA pulldown, siRNA depletion, viral replication assay\",\n      \"pmids\": [\"31647415\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of m6A recognition by the Tudor aromatic cage was not crystallographically resolved\", \"Overlap between m6A reading and methylarginine reading by the same cage was not dissected\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"SND1 was shown to associate with the ER membrane via SEC61A and redirect nascent MHC-I heavy chains to ERAD, mechanistically explaining how SND1 suppresses antigen presentation and promotes tumor immune evasion.\",\n      \"evidence\": \"Subcellular fractionation, co-IP with SEC61A, ERAD assay, SND1-deletion tumor models, flow cytometry\",\n      \"pmids\": [\"32917674\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SND1-dependent ERAD targets other ER client proteins was untested\", \"How SND1 distinguishes MHC-I heavy chains from other SEC61A substrates was unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The MTDH–SND1 complex was shown to destabilize Tap1/2 mRNAs, providing a second, RNA-level mechanism of immune evasion; small-molecule disruptors of the complex restored antigen presentation and synergized with checkpoint immunotherapy, translating structural knowledge into a therapeutic strategy.\",\n      \"evidence\": \"RIP, mRNA stability assay, small-molecule PPI inhibitors (C26-A6), mouse tumor models, anti-PD-1 combination\",\n      \"pmids\": [\"35121988\", \"35121987\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Clinical pharmacology and in-human efficacy of PPI inhibitors remain to be established\", \"Whether additional immune-related mRNAs are regulated by the complex genome-wide was not fully mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"An N-terminal mitochondrial targeting sequence (aa 1–63) was identified that directs SND1 import via TOM70 into mitochondria, where it promotes PGAM5–DRP1-dependent mitophagy, revealing a previously unrecognized mitochondrial function.\",\n      \"evidence\": \"Organelle isolation, IP-MS identifying PGAM5, MTS-deletion construct, co-IP, xenograft\",\n      \"pmids\": [\"35433434\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Independent replication of TOM70-dependent import in a second system is needed\", \"How the same N-terminal region directs SND1 to both ER (SEC61A) and mitochondria (TOM70) was not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"SND1's role as a host factor for viral RNA synthesis was demonstrated for SARS-CoV-2, where SND1 binds the 5′ end of negative-sense viral RNA, interacts with NSP9, and remodels replication-transcription initiation, generalizing its pro-viral RNA function beyond flaviviruses.\",\n      \"evidence\": \"eCLIP, RNA pulldown, co-IP with NSP9, SND1 depletion, cryo-EM of replication organelles, viral growth assays\",\n      \"pmids\": [\"37794589\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SND1's nuclease activity contributes to viral RNA processing was not tested\", \"Broad-spectrum antiviral potential of targeting SND1 was not assessed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include how SND1 is partitioned among its ER, mitochondrial, nuclear, and cytosolic pools; how the same Tudor aromatic cage distinguishes m6A-RNA from methylarginine-protein substrates in a context-dependent manner; and whether the nuclease and m6A-reader functions cooperate or compete on shared RNA targets.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No quantitative model of SND1 subcellular partitioning or its regulatory determinants\", \"Structural basis of dual m6A-RNA and methylarginine-protein recognition by the Tudor cage not resolved\", \"Integrated transcriptome-wide map of SND1 nuclease vs. stabilizer activities lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 11, 23]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [7, 8, 15, 16, 25, 26]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [18]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 9, 12]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [12, 19, 20]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 11, 23]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [19, 20]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [24]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 11, 23]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [2, 7, 8, 9, 18, 25]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [12, 13]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [12, 17]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [24]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [4, 5, 6, 14]}\n    ],\n    \"complexes\": [\n      \"MTDH-SND1 complex\",\n      \"spliceosome (U5 snRNP-associated)\"\n    ],\n    \"partners\": [\n      \"MTDH\",\n      \"STAT6\",\n      \"PIM1\",\n      \"GCN5\",\n      \"UPF1\",\n      \"SAM68\",\n      \"SEC61A1\",\n      \"PGAM5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"SND1 is a multidomain RNA- and protein-binding scaffold that integrates transcriptional coactivation, pre-mRNA splicing, mRNA stability control, and immune evasion across nuclear, cytoplasmic, ER-membrane, and mitochondrial compartments. In the nucleus, SND1 bridges sequence-specific transcription factors (STAT6, c-Myb, Smad2/3/4) to RNA polymerase II and recruits the histone acetyltransferase GCN5 to target promoters, while its Tudor (TSN) domain engages methylated spliceosomal snRNP components to accelerate spliceosome assembly and direct alternative splicing of transcripts such as CD44 in concert with SAM68 [PMID:12234934, PMID:28263968, PMID:17576664, PMID:23995791]. SND1 functions as an N6-methyladenosine (m⁶A) RNA reader that stabilizes both viral (KSHV ORF50, SARS-CoV-2) and cellular (Nrf2, AT1R) transcripts, and as a Tudor-domain nuclease that, together with UPF1, degrades AGO2-loaded miRNAs via TumiD [PMID:31647415, PMID:37794589, PMID:28827400, PMID:18603592]. At the endoplasmic reticulum, SND1 is anchored through SEC61A and diverts nascent MHC-I heavy chains to ERAD, while its complex with MTDH destabilizes Tap1/2 mRNAs, jointly suppressing antigen presentation — a mechanism now pharmacologically targetable with small-molecule inhibitors that synergize with anti-PD-1 immunotherapy [PMID:32917674, PMID:35121988, PMID:35121987].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing SND1 as a transcriptional coactivator: SND1 was linked to signal-dependent gene activation when it was shown to form a Pim-1-phosphorylated complex that potentiates c-Myb transcriptional activity downstream of Ras signaling.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro kinase assay, co-IP, and reporter assays in mammalian cells\",\n      \"pmids\": [\"9809063\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation sites on SND1 by Pim-1 not mapped\", \"Whether phosphorylation is required for coactivator function was not tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The coactivator mechanism was generalized when SND1's SN-like domain was shown to bridge STAT6 to RNA polymerase II, establishing it as a modular adaptor for cytokine-induced transcription.\",\n      \"evidence\": \"Reciprocal co-IP, in vitro binding, domain mapping, IL-4-induced Igε reporter assay\",\n      \"pmids\": [\"12234934\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of SN-domain interaction with STAT6 TAD not resolved\", \"Whether other STATs use the same interface was untested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"SND1 was revealed to have a dual nuclear function — beyond transcription, its Tudor (TSN) domain directly accelerates spliceosome assembly by engaging methylated snRNP components, a mechanism explained at atomic resolution by crystallography.\",\n      \"evidence\": \"In vitro reconstituted splicing assay with purified SND1/TSN domain; X-ray crystal structure of TSN domain with snRNP peptides\",\n      \"pmids\": [\"17576664\", \"17632523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of specific snRNP methylation marks required in vivo not defined\", \"Relative contribution of splicing vs. transcription roles to cellular phenotype unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"SND1 was shown to possess an RISC/AGO2-independent mRNA-stabilizing activity, binding the AT1R 3′-UTR via its SN domains to reduce mRNA decay and enhance translation, broadening its function to post-transcriptional gene regulation.\",\n      \"evidence\": \"RNA pull-down, mRNA decay assay, overexpression/knockdown, domain deletion mapping\",\n      \"pmids\": [\"18603592\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Transcriptome-wide scope of SND1-mediated mRNA stabilization not yet mapped\", \"Mechanism by which SN domains protect mRNA from decay not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The discovery of the MTDH–SND1 interaction established SND1 as a key oncogenic effector: the complex promotes lung metastasis and sustains tumor-initiating cells in breast cancer.\",\n      \"evidence\": \"Mass spectrometry interactome, co-IP, shRNA knockdown, in vivo metastasis assay in mouse models\",\n      \"pmids\": [\"21478147\", \"24981741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How MTDH stabilizes SND1 at the molecular level was not resolved at this stage\", \"Cell-type specificity of MTDH-SND1 oncogenic function unexplored\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The structural basis of the MTDH–SND1 complex was determined at high resolution, revealing a two-tryptophan anchor of MTDH in the SN1/2 groove of SND1 — providing the template for pharmacological disruption.\",\n      \"evidence\": \"X-ray crystallography, site-directed mutagenesis with functional validation in cancer cells\",\n      \"pmids\": [\"25242325\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous post-translational modifications modulate the interface was unknown\", \"No small-molecule inhibitors yet existed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"SND1's splicing function was connected to cancer biology when it was shown to recruit SAM68 and spliceosomal components to CD44 pre-mRNA, promoting inclusion of variable exons that drive prostate cancer cell proliferation and migration.\",\n      \"evidence\": \"Reciprocal co-IP, RNA immunoprecipitation, alternative splicing RT-PCR, siRNA knockdown with migration/proliferation assays\",\n      \"pmids\": [\"23995791\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full set of SND1-regulated alternative splicing events in cancer not catalogued\", \"Whether SAM68 is required for all SND1 splicing targets unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"SND1 was placed within the TGFβ signaling cascade: Smad2/3 directly activates SND1 transcription, and SND1 in turn promotes Smurf1-mediated RhoA degradation, connecting SND1 to cytoskeletal remodeling and metastasis.\",\n      \"evidence\": \"ChIP on SND1 promoter, reporter assay, co-IP, siRNA epistasis, in vivo metastasis model\",\n      \"pmids\": [\"25596283\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SND1 directly activates Smurf1 transcription or acts post-transcriptionally was not resolved\", \"Generalizability beyond breast cancer metastasis models untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The nuclease activity of SND1 was functionally contextualized: SND1's Tudor domain cooperates with UPF1 to degrade AGO2-loaded miRNAs (TumiD), with ~50% of TumiD targets being UPF1-dependent, linking SND1-mediated miRNA decay to cancer cell invasion.\",\n      \"evidence\": \"In vitro nuclease reconstitution with AGO2-loaded miRNAs, genome-wide miR-seq, siRNA knockdown, cell invasion assay\",\n      \"pmids\": [\"28827400\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how UPF1 renders miRNAs accessible to SND1 nuclease activity unresolved\", \"In vivo physiological relevance of TumiD in non-cancer contexts unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"SND1's transcriptional coactivation mechanism was further refined: the Tudor domain recruits GCN5 to Smad promoters, increasing H3K9 acetylation and creating a positive feedback loop within TGFβ signaling.\",\n      \"evidence\": \"EMSA for direct DNA binding, GST pulldown for Tudor-GCN5 interaction, ChIP for H3K9ac, siRNA knockdown\",\n      \"pmids\": [\"28263968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SND1-GCN5 recruitment extends beyond Smad promoters not mapped genome-wide\", \"Structural details of Tudor-GCN5 interface unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"SND1 was identified as an m⁶A RNA reader, establishing a new molecular activity: SND1 preferentially binds m⁶A-modified RNAs including KSHV ORF50 to stabilize them, a function essential for viral lytic replication.\",\n      \"evidence\": \"RIP-seq, eCLIP, m⁶A-modified vs. unmodified RNA pulldown, siRNA knockdown with viral replication assay\",\n      \"pmids\": [\"31647415\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for m⁶A recognition by SND1 not determined\", \"Whether m⁶A reading uses the same domain as other RNA-binding activities was unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"SND1 was found to suppress antigen presentation from the ER: anchored to the ER membrane via SEC61A, it diverts nascent MHC-I heavy chains to ERAD, and its deletion in tumor-bearing mice restores surface MHC-I and increases CD8⁺ T cell infiltration.\",\n      \"evidence\": \"Subcellular fractionation, co-IP with SEC61A and MHC-I HC, ERAD assay, in vivo OT-I mouse model, flow cytometry\",\n      \"pmids\": [\"32917674\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SND1 acts catalytically or as a chaperone in ERAD not distinguished\", \"Relationship between ER-localized SND1 and nuclear SND1 pools not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The MTDH–SND1 complex was shown to suppress antigen presentation through a second, RNA-level mechanism — destabilizing Tap1/2 mRNAs — and small-molecule disruptors of this complex synergized with anti-PD-1 therapy, validating pharmacological targetability.\",\n      \"evidence\": \"Small-molecule PPI inhibitors (C26-A6), RIP for Tap1/2 mRNAs, mRNA stability assay, FACS, genetic mouse models, combination immunotherapy in vivo\",\n      \"pmids\": [\"35121988\", \"35121987\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Selectivity and pharmacokinetic profiles of C26 compounds for clinical translation incomplete\", \"Whether Tap1/2 mRNA destabilization requires m⁶A reading function not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"SND1 was localized to mitochondria via an N-terminal targeting sequence imported through TOM70, where it interacts with PGAM5 to facilitate DRP1-dependent mitophagy under stress — adding a mitochondrial dimension to its functions.\",\n      \"evidence\": \"Mitochondrial fractionation, IP-MS, MTS deletion mutant, FCCP-induced mitophagy assay, in vivo tumor growth\",\n      \"pmids\": [\"35433434\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How the same N-terminal sequence mediates both ER anchoring and mitochondrial import is unresolved\", \"Whether mitochondrial SND1 retains RNA-binding or nuclease activity unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"SND1 was established as a host factor essential for SARS-CoV-2 RNA synthesis: it binds the 5′-end of negative-sense viral RNA, directly interacts with NSP9, and remodels NSP9 occupancy at replication-transcription initiation sites.\",\n      \"evidence\": \"iCLIP/eCLIP, co-IP with NSP9, siRNA depletion with viral kinetics and EM of replication organelles\",\n      \"pmids\": [\"37794589\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SND1's m⁶A-reading function contributes to SARS-CoV-2 RNA binding not resolved\", \"Structural basis of SND1-NSP9 interaction unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include: how a single protein distributes among nuclear, ER, and mitochondrial pools; the structural basis of m⁶A recognition; and whether the nuclease, m⁶A-reading, and mRNA-stabilizing activities are executed by the same or distinct domain configurations.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unified model for SND1 subcellular partitioning\", \"m⁶A reader domain identity not structurally defined\", \"Relative contributions of SND1's multiple activities to tumorigenesis not dissected genetically in a single system\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [2, 5, 6, 14, 16, 21, 22]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 13, 26]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [23]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [17, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 2, 3, 13, 26]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [17, 25]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4, 5, 25]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [20]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [25]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 13, 26]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [2, 8, 14, 23]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [17, 18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [11, 15]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [17, 12]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [20]}\n    ],\n    \"complexes\": [\n      \"MTDH-SND1 complex\",\n      \"RISC\",\n      \"TumiD (TSN-UPF1 miRNA decay complex)\"\n    ],\n    \"partners\": [\n      \"MTDH\",\n      \"SAM68\",\n      \"GCN5\",\n      \"UPF1\",\n      \"SEC61A1\",\n      \"PGAM5\",\n      \"STAT6\",\n      \"PIM1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}