{"gene":"SPSB1","run_date":"2026-06-10T07:46:41","timeline":{"discoveries":[{"year":2017,"finding":"SPSB1 acts as an E3 ubiquitin ligase adaptor that, upon EGF stimulation, recruits Elongin B/C-Cullin complexes to conjugate lysine 29-linked polyubiquitin chains onto hnRNP A1, a splicing regulator, leading to altered alternative splicing of Rac1 (producing Rac1b isoform) and promoting cell migration.","method":"Co-immunoprecipitation, ubiquitylation assays, RNA splicing analysis, RNAi knockdown, cell migration assays","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, ubiquitylation assay, splicing readout, and functional migration assay in a single study with multiple orthogonal methods","pmids":["28084329"],"is_preprint":false},{"year":2010,"finding":"SPSB1 binds substrate peptides via its SPRY domain using a consensus motif (ELNNNL in Par-4; DINNNN in Drosophila VASA). Crystal structures of SPSB1, SPSB2, and SPSB4 revealed the structural basis for substrate recognition; mutation of each of the three Asn residues in Par-4 abrogated binding to all three SPSB proteins.","method":"X-ray crystallography, NMR chemical shift perturbation, site-directed mutagenesis, binding affinity measurements","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures solved, mutagenesis validated binding, NMR confirmation, multiple orthogonal methods in one rigorous study","pmids":["20561531"],"is_preprint":false},{"year":2011,"finding":"SPSB1 interacts with inducible nitric oxide synthase (iNOS) and negatively regulates iNOS protein levels and NO production downstream of TLR3 and TLR4 signaling via a proteasome-dependent mechanism, acting as part of a negative-feedback loop.","method":"SPSB1 transgenic mouse macrophages, shRNA knockdown, co-immunoprecipitation, NO production assays, proteasome inhibitor experiments","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, genetic gain- and loss-of-function in primary macrophages, proteasome dependence confirmed, multiple orthogonal methods","pmids":["21876038"],"is_preprint":false},{"year":2015,"finding":"SPSB1 negatively regulates the TGF-β signaling pathway by interacting with TGF-β type II receptor (TβRII) — but not TβRI — via its SPRY domain, co-localizing with TβRII on the cell membrane, and promoting TβRII ubiquitination and proteasomal degradation via its SOCS box. siRNA-mediated silencing of SPSB1 enhanced TGF-β signaling, cell migration, and invasion.","method":"Co-immunoprecipitation, immunofluorescence co-localization, ubiquitination assay, siRNA knockdown, TGF-β reporter assay, migration/invasion assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, ubiquitination assay, co-localization imaging, and functional siRNA knockdown with multiple readouts in one study","pmids":["26032413"],"is_preprint":false},{"year":2005,"finding":"SPSB1 (SSB-1) binds to the MET receptor tyrosine kinase through its SPRY domain in both basal and HGF-stimulated conditions. HGF stimulation recruits more SPSB1 to MET and induces SPSB1 phosphorylation at tyrosine 31. Overexpression of SPSB1 enhances HGF-induced Erk phosphorylation and Elk-1/SRE activation; RNAi knockdown reduces these responses. Phosphorylated SPSB1 binds p120RasGAP but does not promote its degradation.","method":"Co-immunoprecipitation, luciferase reporter assays (SRE), RNAi knockdown, Western blot (Erk phosphorylation), tyrosine phosphorylation analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, functional reporter assays, RNAi, single lab with multiple orthogonal methods","pmids":["15713673"],"is_preprint":false},{"year":2014,"finding":"SPSB1 potentiates c-MET signaling to protect tumor cells from apoptosis induced by HER2/neu pathway inhibition or chemotherapy, promoting breast cancer recurrence in genetically engineered mouse models. SPSB1 overexpression is sufficient to promote tumor recurrence and necessary for it.","method":"Genetically engineered mouse models, gain- and loss-of-function experiments, apoptosis assays, c-MET signaling pathway analysis","journal":"Cancer discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo mouse models with gain/loss-of-function, defined molecular pathway, single lab","pmids":["24786206"],"is_preprint":false},{"year":2019,"finding":"SPSB1 directly interacts with p21 and promotes its ubiquitin-mediated proteasomal degradation, thereby destabilizing p21 and enhancing ovarian cancer cell survival and migration.","method":"Co-immunoprecipitation, ubiquitination assay, protein stability assay, siRNA knockdown, cell viability and migration assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination and protein stability assays, functional knockdown, single lab","pmids":["30712944"],"is_preprint":false},{"year":2019,"finding":"SPSB1 and its paralog SPSB4, but not SPSB2 or SPSB3, interact with the circadian clock protein RevErbα and facilitate its ubiquitination and proteasomal degradation, thereby regulating circadian period length.","method":"Cell-based functional ubiquitin ligase screen, co-immunoprecipitation, ubiquitination assay, circadian period measurement","journal":"Journal of biological rhythms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assay, functional circadian readout, single lab","pmids":["31607207"],"is_preprint":false},{"year":2018,"finding":"Ras interacts with the SPRY domain of SPSB1 and co-localizes with SPSB1 on the cell membrane, promoting SPSB1 protein degradation via enhanced mono- and di-ubiquitination. Reduced SPSB1 stabilizes TβRII, enhancing Smad2/3 phosphorylation and TGF-β signaling. Forced SPSB1 expression in Ras-transformed cells suppresses TGF-β signaling and migration/invasion.","method":"Co-immunoprecipitation, immunofluorescence co-localization, ubiquitination assay, luciferase reporter assay, transwell migration/invasion assay","journal":"Cell communication and signaling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, ubiquitination assay, co-localization, functional assays, single lab","pmids":["29534718"],"is_preprint":false},{"year":2020,"finding":"SPSB1 acts as a negative regulator of NF-κB activation downstream of multiple signaling pathways (TLRs, RNA and DNA sensing adaptors) via its SOCS-box domain. SPSB1 co-precipitates with the NF-κB subunit p65 at both overexpressed and endogenous levels but does not affect IκBα phosphorylation/degradation or p65 nuclear translocation, suggesting inhibition at or downstream of the NF-κB heterodimer level.","method":"Systematic siRNA depletion of SOCS-box proteins, NF-κB luciferase reporter assay, overexpression, co-immunoprecipitation (endogenous and overexpressed), p65 nuclear translocation imaging, cytokine measurement","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic screen confirmed by multiple orthogonal assays, endogenous Co-IP, single lab","pmids":["32038638"],"is_preprint":false},{"year":2023,"finding":"SPSB1 interacts with TβRII via its SPRY domain and promotes TβRII ubiquitination and destabilization via its SOCS box, impairing TβRII-Akt-Myogenin signaling and protein synthesis in myocytes. Inflammatory cytokines (TNF, IL-1β, IL-6) upregulate SPSB1 via NF-κB and gp130/JAK2/STAT3 pathways. AAV9-shRNA-mediated Spsb1 knockdown in vivo attenuated muscle atrophy in septic mice.","method":"Co-immunoprecipitation, ubiquitination assay, protein half-life assay, protein synthesis assay, immunocytochemistry, retroviral overexpression, AAV9-shRNA in vivo knockdown, qRT-PCR, Western blot","journal":"Journal of cachexia, sarcopenia and muscle","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal mechanistic assays (Co-IP, ubiquitination, half-life, protein synthesis), in vivo rescue with AAV9-shRNA, pathway dissection across multiple cell types","pmids":["37209006"],"is_preprint":false},{"year":2026,"finding":"SPSB1 ubiquitinates and destabilizes the transcription factor KLF6, thereby relieving KLF6-mediated transcriptional promotion of PD-L1. SPSB1 loss leads to KLF6 stabilization, increased PD-L1 expression, and T cell exhaustion. Upstream, PTBP3 binds the SPSB1 3'UTR to stabilize its mRNA.","method":"siRNA/shRNA knockdown, ubiquitination assay, co-culture T cell exhaustion assay, in vivo mouse tumor models, rescue experiments, mRNA stability assay","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ubiquitination assay, functional rescue, in vivo confirmation, single lab","pmids":["42055144"],"is_preprint":false}],"current_model":"SPSB1 is an E3 ubiquitin ligase adaptor protein containing a substrate-recognition SPRY domain and a SOCS box that recruits Elongin B/C-Cullin-5/Rbx-2 complexes; it targets multiple substrates for ubiquitin-mediated proteasomal degradation — including hnRNP A1 (via K29-linked chains, regulating alternative splicing and EGF-driven cell migration), iNOS (controlling NO production downstream of TLR3/4), TGF-β type II receptor TβRII (negatively regulating TGF-β/Smad signaling and myogenic differentiation), p21 (promoting cancer cell survival), RevErbα (regulating circadian period), and KLF6 (modulating PD-L1 expression) — and additionally co-precipitates with p65 to suppress NF-κB activity and interacts with MET to enhance HGF-induced Erk-Elk-1-SRE signaling."},"narrative":{"mechanistic_narrative":"SPSB1 is a substrate-recognition adaptor of Cullin-RING E3 ubiquitin ligase complexes that couples a SPRY substrate-binding domain to a SOCS box recruiting Elongin B/C-Cullin modules, directing diverse substrates to ubiquitin-mediated proteasomal degradation [PMID:28084329, PMID:20561531]. Its SPRY domain recognizes substrates through a conserved Asn-rich consensus motif, with all three core asparagines required for binding [PMID:20561531]. Through this activity SPSB1 negatively regulates signaling across multiple processes: it destabilizes the TGF-β type II receptor TβRII (but not TβRI), dampening TGF-β/Smad-driven migration and invasion and, in myocytes, TβRII-Akt-Myogenin-dependent protein synthesis during inflammatory muscle atrophy [PMID:26032413, PMID:37209006]; it limits inducible nitric oxide synthase levels and NO output downstream of TLR3/TLR4 as a negative-feedback brake [PMID:21876038]; and it suppresses NF-κB activity through association with the p65 subunit at or downstream of the heterodimer [PMID:32038638]. SPSB1 further ubiquitinates the splicing regulator hnRNP A1 via K29-linked chains upon EGF stimulation, shifting Rac1 alternative splicing toward Rac1b and promoting migration [PMID:28084329], destabilizes p21 to enhance cancer cell survival [PMID:30712944], degrades the circadian repressor RevErbα to set period length [PMID:31607207], and destabilizes the transcription factor KLF6 to restrain PD-L1 expression and prevent T cell exhaustion [PMID:42055144]. Independent of its degradative role, SPSB1 binds the MET receptor tyrosine kinase through its SPRY domain, is tyrosine-phosphorylated upon HGF stimulation, and potentiates HGF-induced Erk-Elk-1-SRE signaling to protect tumor cells from apoptosis [PMID:15713673, PMID:24786206]. SPSB1 abundance is itself controlled, being degraded upon Ras-driven ubiquitination and stabilized by PTBP3 binding to its 3'UTR [PMID:29534718, PMID:42055144].","teleology":[{"year":2005,"claim":"Established the first SPSB1 binding partner and an unexpected non-degradative signaling role, linking SPSB1 to receptor tyrosine kinase output.","evidence":"Co-IP, SRE luciferase reporters, RNAi, and tyrosine phosphorylation analysis in HGF-stimulated cells","pmids":["15713673"],"confidence":"Medium","gaps":["Mechanism by which SPSB1 enhances Erk-Elk-1 signaling without degrading MET or p120RasGAP unresolved","Functional consequence of Y31 phosphorylation not defined"]},{"year":2010,"claim":"Defined the structural and sequence basis for SPSB substrate recognition, showing the SPRY domain reads a conserved Asn-rich motif.","evidence":"X-ray crystallography of SPSB1/2/4, NMR, and mutagenesis of Par-4 binding motif","pmids":["20561531"],"confidence":"High","gaps":["Did not establish which endogenous substrates use this motif in cells","No ubiquitination or degradation readout"]},{"year":2011,"claim":"Demonstrated SPSB1 functions as a degradative adaptor in innate immunity, targeting iNOS to limit NO as a negative-feedback control.","evidence":"Transgenic mouse macrophages, shRNA, reciprocal Co-IP, NO assays, and proteasome inhibition","pmids":["21876038"],"confidence":"High","gaps":["Direct ubiquitination of iNOS by an SPSB1-containing ligase not biochemically reconstituted","Lysine linkage type not defined"]},{"year":2014,"claim":"Placed SPSB1 in a disease context, showing it potentiates c-MET signaling to drive breast cancer recurrence and survival.","evidence":"Genetically engineered mouse models with gain/loss-of-function and apoptosis assays","pmids":["24786206"],"confidence":"Medium","gaps":["Molecular link between SPSB1 and c-MET potentiation mechanistically distinct from its E3 adaptor role unclear","Single lab"]},{"year":2015,"claim":"Identified TβRII as a degradation substrate, defining SPSB1 as a negative regulator of TGF-β/Smad signaling and invasion.","evidence":"Co-IP, co-localization imaging, ubiquitination assay, siRNA, and reporter/migration assays","pmids":["26032413"],"confidence":"High","gaps":["Receptor selectivity (TβRII not TβRI) structural basis not resolved","In vivo relevance not tested in this study"]},{"year":2017,"claim":"Showed SPSB1 links EGF signaling to splicing control, ubiquitinating hnRNP A1 with atypical K29 chains to reprogram Rac1 splicing and migration.","evidence":"Co-IP, ubiquitylation assays, splicing analysis, RNAi, and migration assays","pmids":["28084329"],"confidence":"High","gaps":["Functional consequence of K29-linked (vs degradative) chains on hnRNP A1 fate not fully dissected","Whether SPSB1 directly determines linkage specificity unknown"]},{"year":2018,"claim":"Revealed SPSB1 itself is a regulated target, with Ras driving its ubiquitination and turnover to relieve TGF-β suppression.","evidence":"Co-IP, co-localization, ubiquitination, reporter, and transwell assays in Ras-transformed cells","pmids":["29534718"],"confidence":"Medium","gaps":["E3 ligase responsible for Ras-induced SPSB1 ubiquitination not identified","Mono/di-ubiquitination role in turnover mechanism incomplete"]},{"year":2019,"claim":"Extended SPSB1 substrate range to p21 and the circadian repressor RevErbα, connecting it to cancer cell survival and clock period control.","evidence":"Co-IP, ubiquitination and stability assays, ligase screen, and circadian period measurement","pmids":["30712944","31607207"],"confidence":"Medium","gaps":["Substrate motif on p21 and RevErbα not mapped","Paralog redundancy (SPSB4) for RevErbα not fully separated functionally"]},{"year":2020,"claim":"Showed SPSB1 restrains NF-κB at or downstream of the p65 heterodimer via its SOCS box, broadening its innate-immune brake function.","evidence":"Systematic SOCS-box siRNA screen, NF-κB reporters, endogenous Co-IP, and translocation imaging","pmids":["32038638"],"confidence":"Medium","gaps":["Whether p65 is a degradation substrate or sequestered partner unresolved","Step downstream of nuclear translocation not pinpointed"]},{"year":2023,"claim":"Established an in vivo pathological role: inflammatory cytokines induce SPSB1 to degrade TβRII and drive sepsis muscle atrophy, reversible by knockdown.","evidence":"Co-IP, ubiquitination, half-life and protein synthesis assays, plus AAV9-shRNA in vivo rescue in septic mice","pmids":["37209006"],"confidence":"High","gaps":["Relative contribution of TβRII degradation vs other substrates to atrophy not quantified"]},{"year":2026,"claim":"Connected SPSB1 to tumor immune evasion, showing it degrades KLF6 to limit PD-L1 and is post-transcriptionally controlled by PTBP3.","evidence":"Knockdown, ubiquitination assay, T cell exhaustion co-culture, in vivo tumor models, and mRNA stability assay","pmids":["42055144"],"confidence":"Medium","gaps":["Direct vs indirect ubiquitination of KLF6 not biochemically isolated","Single lab"]},{"year":null,"claim":"How SPSB1 selects among its many substrates in a given cell context, and what governs whether it builds degradative versus non-degradative ubiquitin chains, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model for context-dependent substrate prioritization","Chain-linkage determinants for K29 vs canonical degradative chains undefined","No structural model of the assembled SPSB1-Cullin-5-substrate ligase"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,3,6,7,10,11]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,3]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,8]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,3,6,7,10,11]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,4,8,10]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,9,11]},{"term_id":"R-HSA-9909396","term_label":"Circadian clock","supporting_discovery_ids":[7]}],"complexes":["Elongin B/C-Cullin-5-Rbx2 E3 ligase"],"partners":["HNRNPA1","NOS2","TGFBR2","MET","CDKN1A","NR1D1","RELA","KLF6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96BD6","full_name":"SPRY domain-containing SOCS box protein 1","aliases":[],"length_aa":273,"mass_kda":30.9,"function":"Substrate recognition component of a SCF-like ECS (Elongin BC-CUL2/5-SOCS-box protein) E3 ubiquitin-protein ligase complex which mediates the ubiquitination and subsequent proteasomal degradation of target proteins (PubMed:15601820, PubMed:21199876). Negatively regulates nitric oxide (NO) production and limits cellular toxicity in activated macrophages by mediating the ubiquitination and proteasomal degradation of NOS2 (PubMed:21199876). Acts as a bridge which links NOS2 with the ECS E3 ubiquitin ligase complex components ELOC and CUL5 (PubMed:21199876)","subcellular_location":"Cytoplasm; Cytoplasm, cytosol","url":"https://www.uniprot.org/uniprotkb/Q96BD6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SPSB1","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SPSB1","total_profiled":1310},"omim":[{"mim_id":"611660","title":"SPRY DOMAIN- AND SOCS BOX-CONTAINING 4; SPSB4","url":"https://www.omim.org/entry/611660"},{"mim_id":"611659","title":"SPRY DOMAIN- AND SOCS BOX-CONTAINING 3; SPSB3","url":"https://www.omim.org/entry/611659"},{"mim_id":"611658","title":"SPRY DOMAIN- AND SOCS BOX-CONTAINING 2; SPSB2","url":"https://www.omim.org/entry/611658"},{"mim_id":"611657","title":"SPRY DOMAIN- AND SOCS BOX-CONTAINING 1; SPSB1","url":"https://www.omim.org/entry/611657"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SPSB1"},"hgnc":{"alias_symbol":["SSB-1"],"prev_symbol":[]},"alphafold":{"accession":"Q96BD6","domains":[{"cath_id":"2.60.120.920","chopping":"9-229","consensus_level":"high","plddt":93.1185,"start":9,"end":229},{"cath_id":"1.10.750","chopping":"236-270","consensus_level":"high","plddt":91.6654,"start":236,"end":270}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96BD6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96BD6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96BD6-F1-predicted_aligned_error_v6.png","plddt_mean":92.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SPSB1","jax_strain_url":"https://www.jax.org/strain/search?query=SPSB1"},"sequence":{"accession":"Q96BD6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96BD6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96BD6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96BD6"}},"corpus_meta":[{"pmid":"6384214","id":"PMC_6384214","title":"Characterization of the structural and functional defect in the Escherichia coli single-stranded DNA binding protein encoded by the ssb-1 mutant gene. Expression of the ssb-1 gene under lambda pL regulation.","date":"1984","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/6384214","citation_count":95,"is_preprint":false},{"pmid":"2121740","id":"PMC_2121740","title":"SSB-1 of the yeast Saccharomyces cerevisiae is a nucleolar-specific, silver-binding protein that is associated with the snR10 and snR11 small nuclear RNAs.","date":"1990","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/2121740","citation_count":82,"is_preprint":false},{"pmid":"1988441","id":"PMC_1988441","title":"Monomer-tetramer equilibrium of the Escherichia coli ssb-1 mutant single strand binding protein.","date":"1991","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/1988441","citation_count":70,"is_preprint":false},{"pmid":"28084329","id":"PMC_28084329","title":"SPSB1-mediated HnRNP A1 ubiquitylation regulates alternative splicing and cell migration in EGF signaling.","date":"2017","source":"Cell research","url":"https://pubmed.ncbi.nlm.nih.gov/28084329","citation_count":65,"is_preprint":false},{"pmid":"20561531","id":"PMC_20561531","title":"Structural basis for Par-4 recognition by the SPRY domain- and SOCS box-containing proteins SPSB1, SPSB2, and SPSB4.","date":"2010","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/20561531","citation_count":54,"is_preprint":false},{"pmid":"21876038","id":"PMC_21876038","title":"TLR regulation of SPSB1 controls inducible nitric oxide synthase induction.","date":"2011","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/21876038","citation_count":53,"is_preprint":false},{"pmid":"7045074","id":"PMC_7045074","title":"Effects of the ssb-1 and ssb-113 mutations on survival and DNA repair in UV-irradiated delta uvrB strains of Escherichia coli K-12.","date":"1982","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/7045074","citation_count":47,"is_preprint":false},{"pmid":"6341603","id":"PMC_6341603","title":"Amplification of ssb-1 mutant single-stranded DNA-binding protein in Escherichia coli.","date":"1983","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/6341603","citation_count":46,"is_preprint":false},{"pmid":"15713673","id":"PMC_15713673","title":"The SPRY domain-containing SOCS box protein 1 (SSB-1) interacts with MET and enhances the hepatocyte growth factor-induced Erk-Elk-1-serum response element pathway.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15713673","citation_count":46,"is_preprint":false},{"pmid":"1988680","id":"PMC_1988680","title":"Monomers of the Escherichia coli SSB-1 mutant protein bind single-stranded DNA.","date":"1991","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/1988680","citation_count":41,"is_preprint":false},{"pmid":"24786206","id":"PMC_24786206","title":"SPSB1 promotes breast cancer recurrence by potentiating c-MET signaling.","date":"2014","source":"Cancer discovery","url":"https://pubmed.ncbi.nlm.nih.gov/24786206","citation_count":38,"is_preprint":false},{"pmid":"26032413","id":"PMC_26032413","title":"SPSB1, a Novel Negative Regulator of the Transforming Growth Factor-β Signaling Pathway Targeting the Type II Receptor.","date":"2015","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/26032413","citation_count":37,"is_preprint":false},{"pmid":"6276686","id":"PMC_6276686","title":"Variable expression of the ssb--1 allele in different strains of Escherichia coli K12 and B: differential suppression of its effects on DNA replication, DNA repair and ultraviolet mutagenesis.","date":"1981","source":"Molecular & general genetics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/6276686","citation_count":37,"is_preprint":false},{"pmid":"6752116","id":"PMC_6752116","title":"Suppression of the ssb-1 and ssb-113 mutations of Escherichia coli by a wild-type rep gene, NaCl, and glucose.","date":"1982","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/6752116","citation_count":29,"is_preprint":false},{"pmid":"2897690","id":"PMC_2897690","title":"Suppression of the Escherichia coli ssb-1 mutation by an allele of groEL.","date":"1988","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/2897690","citation_count":17,"is_preprint":false},{"pmid":"37209006","id":"PMC_37209006","title":"SPSB1-mediated inhibition of TGF-β receptor-II impairs myogenesis in inflammation.","date":"2023","source":"Journal of cachexia, sarcopenia and muscle","url":"https://pubmed.ncbi.nlm.nih.gov/37209006","citation_count":16,"is_preprint":false},{"pmid":"29534718","id":"PMC_29534718","title":"Ras enhances TGF-β signaling by decreasing cellular protein levels of its type II receptor negative regulator SPSB1.","date":"2018","source":"Cell communication and signaling : CCS","url":"https://pubmed.ncbi.nlm.nih.gov/29534718","citation_count":15,"is_preprint":false},{"pmid":"30712944","id":"PMC_30712944","title":"SPSB1 enhances ovarian cancer cell survival by destabilizing p21.","date":"2019","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/30712944","citation_count":12,"is_preprint":false},{"pmid":"32038638","id":"PMC_32038638","title":"Cullin-5 Adaptor SPSB1 Controls NF-κB Activation Downstream of Multiple Signaling Pathways.","date":"2020","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/32038638","citation_count":10,"is_preprint":false},{"pmid":"19184407","id":"PMC_19184407","title":"Cloning and characterization of the SSB-1 and SSB-4 genes expressed in zebrafish gonads.","date":"2009","source":"Biochemical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19184407","citation_count":10,"is_preprint":false},{"pmid":"2964522","id":"PMC_2964522","title":"Differential suppressor effects of the ssb-1 and ssb-113 alleles on uvrD mutator of Escherichia coli in DNA repair and mutagenesis.","date":"1987","source":"Journal of basic microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/2964522","citation_count":10,"is_preprint":false},{"pmid":"31607207","id":"PMC_31607207","title":"The E3 Ligases Spsb1 and Spsb4 Regulate RevErbα Degradation and Circadian Period.","date":"2019","source":"Journal of biological rhythms","url":"https://pubmed.ncbi.nlm.nih.gov/31607207","citation_count":8,"is_preprint":false},{"pmid":"40226024","id":"PMC_40226024","title":"Testis-enriched Spsb1 is not required for spermatogenesis and fertility in mice.","date":"2025","source":"American journal of translational research","url":"https://pubmed.ncbi.nlm.nih.gov/40226024","citation_count":1,"is_preprint":false},{"pmid":"41146881","id":"PMC_41146881","title":"Novel variants in ARID1B, SPSB1, and RAET1-AS shape genetic susceptibility and protection in systemic lupus erythematosus and lupus nephritis.","date":"2025","source":"Journal of translational autoimmunity","url":"https://pubmed.ncbi.nlm.nih.gov/41146881","citation_count":0,"is_preprint":false},{"pmid":"42055144","id":"PMC_42055144","title":"SPSB1 inhibition induces cancer immune evasion by modulating the KLF6/PD-L1 axis in non-small cell lung cancer cells.","date":"2026","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/42055144","citation_count":0,"is_preprint":false},{"pmid":"42046907","id":"PMC_42046907","title":"Expanding the Fish-Brain Invitrome With the Senegalese Sole SsB-1 Cell Line-A Versatile Model for Neurotropic Virus Research.","date":"2026","source":"Journal of fish diseases","url":"https://pubmed.ncbi.nlm.nih.gov/42046907","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15361,"output_tokens":3347,"usd":0.048144,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10883,"output_tokens":4039,"usd":0.077695,"stage2_stop_reason":"end_turn"},"total_usd":0.125839,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"SPSB1 acts as an E3 ubiquitin ligase adaptor that, upon EGF stimulation, recruits Elongin B/C-Cullin complexes to conjugate lysine 29-linked polyubiquitin chains onto hnRNP A1, a splicing regulator, leading to altered alternative splicing of Rac1 (producing Rac1b isoform) and promoting cell migration.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitylation assays, RNA splicing analysis, RNAi knockdown, cell migration assays\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, ubiquitylation assay, splicing readout, and functional migration assay in a single study with multiple orthogonal methods\",\n      \"pmids\": [\"28084329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SPSB1 binds substrate peptides via its SPRY domain using a consensus motif (ELNNNL in Par-4; DINNNN in Drosophila VASA). Crystal structures of SPSB1, SPSB2, and SPSB4 revealed the structural basis for substrate recognition; mutation of each of the three Asn residues in Par-4 abrogated binding to all three SPSB proteins.\",\n      \"method\": \"X-ray crystallography, NMR chemical shift perturbation, site-directed mutagenesis, binding affinity measurements\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures solved, mutagenesis validated binding, NMR confirmation, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"20561531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SPSB1 interacts with inducible nitric oxide synthase (iNOS) and negatively regulates iNOS protein levels and NO production downstream of TLR3 and TLR4 signaling via a proteasome-dependent mechanism, acting as part of a negative-feedback loop.\",\n      \"method\": \"SPSB1 transgenic mouse macrophages, shRNA knockdown, co-immunoprecipitation, NO production assays, proteasome inhibitor experiments\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, genetic gain- and loss-of-function in primary macrophages, proteasome dependence confirmed, multiple orthogonal methods\",\n      \"pmids\": [\"21876038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SPSB1 negatively regulates the TGF-β signaling pathway by interacting with TGF-β type II receptor (TβRII) — but not TβRI — via its SPRY domain, co-localizing with TβRII on the cell membrane, and promoting TβRII ubiquitination and proteasomal degradation via its SOCS box. siRNA-mediated silencing of SPSB1 enhanced TGF-β signaling, cell migration, and invasion.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence co-localization, ubiquitination assay, siRNA knockdown, TGF-β reporter assay, migration/invasion assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, ubiquitination assay, co-localization imaging, and functional siRNA knockdown with multiple readouts in one study\",\n      \"pmids\": [\"26032413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SPSB1 (SSB-1) binds to the MET receptor tyrosine kinase through its SPRY domain in both basal and HGF-stimulated conditions. HGF stimulation recruits more SPSB1 to MET and induces SPSB1 phosphorylation at tyrosine 31. Overexpression of SPSB1 enhances HGF-induced Erk phosphorylation and Elk-1/SRE activation; RNAi knockdown reduces these responses. Phosphorylated SPSB1 binds p120RasGAP but does not promote its degradation.\",\n      \"method\": \"Co-immunoprecipitation, luciferase reporter assays (SRE), RNAi knockdown, Western blot (Erk phosphorylation), tyrosine phosphorylation analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, functional reporter assays, RNAi, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"15713673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SPSB1 potentiates c-MET signaling to protect tumor cells from apoptosis induced by HER2/neu pathway inhibition or chemotherapy, promoting breast cancer recurrence in genetically engineered mouse models. SPSB1 overexpression is sufficient to promote tumor recurrence and necessary for it.\",\n      \"method\": \"Genetically engineered mouse models, gain- and loss-of-function experiments, apoptosis assays, c-MET signaling pathway analysis\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo mouse models with gain/loss-of-function, defined molecular pathway, single lab\",\n      \"pmids\": [\"24786206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPSB1 directly interacts with p21 and promotes its ubiquitin-mediated proteasomal degradation, thereby destabilizing p21 and enhancing ovarian cancer cell survival and migration.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, protein stability assay, siRNA knockdown, cell viability and migration assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination and protein stability assays, functional knockdown, single lab\",\n      \"pmids\": [\"30712944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPSB1 and its paralog SPSB4, but not SPSB2 or SPSB3, interact with the circadian clock protein RevErbα and facilitate its ubiquitination and proteasomal degradation, thereby regulating circadian period length.\",\n      \"method\": \"Cell-based functional ubiquitin ligase screen, co-immunoprecipitation, ubiquitination assay, circadian period measurement\",\n      \"journal\": \"Journal of biological rhythms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assay, functional circadian readout, single lab\",\n      \"pmids\": [\"31607207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Ras interacts with the SPRY domain of SPSB1 and co-localizes with SPSB1 on the cell membrane, promoting SPSB1 protein degradation via enhanced mono- and di-ubiquitination. Reduced SPSB1 stabilizes TβRII, enhancing Smad2/3 phosphorylation and TGF-β signaling. Forced SPSB1 expression in Ras-transformed cells suppresses TGF-β signaling and migration/invasion.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence co-localization, ubiquitination assay, luciferase reporter assay, transwell migration/invasion assay\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, ubiquitination assay, co-localization, functional assays, single lab\",\n      \"pmids\": [\"29534718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SPSB1 acts as a negative regulator of NF-κB activation downstream of multiple signaling pathways (TLRs, RNA and DNA sensing adaptors) via its SOCS-box domain. SPSB1 co-precipitates with the NF-κB subunit p65 at both overexpressed and endogenous levels but does not affect IκBα phosphorylation/degradation or p65 nuclear translocation, suggesting inhibition at or downstream of the NF-κB heterodimer level.\",\n      \"method\": \"Systematic siRNA depletion of SOCS-box proteins, NF-κB luciferase reporter assay, overexpression, co-immunoprecipitation (endogenous and overexpressed), p65 nuclear translocation imaging, cytokine measurement\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic screen confirmed by multiple orthogonal assays, endogenous Co-IP, single lab\",\n      \"pmids\": [\"32038638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SPSB1 interacts with TβRII via its SPRY domain and promotes TβRII ubiquitination and destabilization via its SOCS box, impairing TβRII-Akt-Myogenin signaling and protein synthesis in myocytes. Inflammatory cytokines (TNF, IL-1β, IL-6) upregulate SPSB1 via NF-κB and gp130/JAK2/STAT3 pathways. AAV9-shRNA-mediated Spsb1 knockdown in vivo attenuated muscle atrophy in septic mice.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, protein half-life assay, protein synthesis assay, immunocytochemistry, retroviral overexpression, AAV9-shRNA in vivo knockdown, qRT-PCR, Western blot\",\n      \"journal\": \"Journal of cachexia, sarcopenia and muscle\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal mechanistic assays (Co-IP, ubiquitination, half-life, protein synthesis), in vivo rescue with AAV9-shRNA, pathway dissection across multiple cell types\",\n      \"pmids\": [\"37209006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"SPSB1 ubiquitinates and destabilizes the transcription factor KLF6, thereby relieving KLF6-mediated transcriptional promotion of PD-L1. SPSB1 loss leads to KLF6 stabilization, increased PD-L1 expression, and T cell exhaustion. Upstream, PTBP3 binds the SPSB1 3'UTR to stabilize its mRNA.\",\n      \"method\": \"siRNA/shRNA knockdown, ubiquitination assay, co-culture T cell exhaustion assay, in vivo mouse tumor models, rescue experiments, mRNA stability assay\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ubiquitination assay, functional rescue, in vivo confirmation, single lab\",\n      \"pmids\": [\"42055144\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SPSB1 is an E3 ubiquitin ligase adaptor protein containing a substrate-recognition SPRY domain and a SOCS box that recruits Elongin B/C-Cullin-5/Rbx-2 complexes; it targets multiple substrates for ubiquitin-mediated proteasomal degradation — including hnRNP A1 (via K29-linked chains, regulating alternative splicing and EGF-driven cell migration), iNOS (controlling NO production downstream of TLR3/4), TGF-β type II receptor TβRII (negatively regulating TGF-β/Smad signaling and myogenic differentiation), p21 (promoting cancer cell survival), RevErbα (regulating circadian period), and KLF6 (modulating PD-L1 expression) — and additionally co-precipitates with p65 to suppress NF-κB activity and interacts with MET to enhance HGF-induced Erk-Elk-1-SRE signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SPSB1 is a substrate-recognition adaptor of Cullin-RING E3 ubiquitin ligase complexes that couples a SPRY substrate-binding domain to a SOCS box recruiting Elongin B/C-Cullin modules, directing diverse substrates to ubiquitin-mediated proteasomal degradation [#0, #1]. Its SPRY domain recognizes substrates through a conserved Asn-rich consensus motif, with all three core asparagines required for binding [#1]. Through this activity SPSB1 negatively regulates signaling across multiple processes: it destabilizes the TGF-\\u03b2 type II receptor T\\u03b2RII (but not T\\u03b2RI), dampening TGF-\\u03b2/Smad-driven migration and invasion and, in myocytes, T\\u03b2RII-Akt-Myogenin-dependent protein synthesis during inflammatory muscle atrophy [#3, #10]; it limits inducible nitric oxide synthase levels and NO output downstream of TLR3/TLR4 as a negative-feedback brake [#2]; and it suppresses NF-\\u03baB activity through association with the p65 subunit at or downstream of the heterodimer [#9]. SPSB1 further ubiquitinates the splicing regulator hnRNP A1 via K29-linked chains upon EGF stimulation, shifting Rac1 alternative splicing toward Rac1b and promoting migration [#0], destabilizes p21 to enhance cancer cell survival [#6], degrades the circadian repressor RevErb\\u03b1 to set period length [#7], and destabilizes the transcription factor KLF6 to restrain PD-L1 expression and prevent T cell exhaustion [#11]. Independent of its degradative role, SPSB1 binds the MET receptor tyrosine kinase through its SPRY domain, is tyrosine-phosphorylated upon HGF stimulation, and potentiates HGF-induced Erk-Elk-1-SRE signaling to protect tumor cells from apoptosis [#4, #5]. SPSB1 abundance is itself controlled, being degraded upon Ras-driven ubiquitination and stabilized by PTBP3 binding to its 3'UTR [#8, #11].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established the first SPSB1 binding partner and an unexpected non-degradative signaling role, linking SPSB1 to receptor tyrosine kinase output.\",\n      \"evidence\": \"Co-IP, SRE luciferase reporters, RNAi, and tyrosine phosphorylation analysis in HGF-stimulated cells\",\n      \"pmids\": [\"15713673\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism by which SPSB1 enhances Erk-Elk-1 signaling without degrading MET or p120RasGAP unresolved\", \"Functional consequence of Y31 phosphorylation not defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the structural and sequence basis for SPSB substrate recognition, showing the SPRY domain reads a conserved Asn-rich motif.\",\n      \"evidence\": \"X-ray crystallography of SPSB1/2/4, NMR, and mutagenesis of Par-4 binding motif\",\n      \"pmids\": [\"20561531\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not establish which endogenous substrates use this motif in cells\", \"No ubiquitination or degradation readout\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated SPSB1 functions as a degradative adaptor in innate immunity, targeting iNOS to limit NO as a negative-feedback control.\",\n      \"evidence\": \"Transgenic mouse macrophages, shRNA, reciprocal Co-IP, NO assays, and proteasome inhibition\",\n      \"pmids\": [\"21876038\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct ubiquitination of iNOS by an SPSB1-containing ligase not biochemically reconstituted\", \"Lysine linkage type not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed SPSB1 in a disease context, showing it potentiates c-MET signaling to drive breast cancer recurrence and survival.\",\n      \"evidence\": \"Genetically engineered mouse models with gain/loss-of-function and apoptosis assays\",\n      \"pmids\": [\"24786206\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Molecular link between SPSB1 and c-MET potentiation mechanistically distinct from its E3 adaptor role unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified T\\u03b2RII as a degradation substrate, defining SPSB1 as a negative regulator of TGF-\\u03b2/Smad signaling and invasion.\",\n      \"evidence\": \"Co-IP, co-localization imaging, ubiquitination assay, siRNA, and reporter/migration assays\",\n      \"pmids\": [\"26032413\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Receptor selectivity (T\\u03b2RII not T\\u03b2RI) structural basis not resolved\", \"In vivo relevance not tested in this study\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed SPSB1 links EGF signaling to splicing control, ubiquitinating hnRNP A1 with atypical K29 chains to reprogram Rac1 splicing and migration.\",\n      \"evidence\": \"Co-IP, ubiquitylation assays, splicing analysis, RNAi, and migration assays\",\n      \"pmids\": [\"28084329\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Functional consequence of K29-linked (vs degradative) chains on hnRNP A1 fate not fully dissected\", \"Whether SPSB1 directly determines linkage specificity unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Revealed SPSB1 itself is a regulated target, with Ras driving its ubiquitination and turnover to relieve TGF-\\u03b2 suppression.\",\n      \"evidence\": \"Co-IP, co-localization, ubiquitination, reporter, and transwell assays in Ras-transformed cells\",\n      \"pmids\": [\"29534718\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"E3 ligase responsible for Ras-induced SPSB1 ubiquitination not identified\", \"Mono/di-ubiquitination role in turnover mechanism incomplete\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended SPSB1 substrate range to p21 and the circadian repressor RevErb\\u03b1, connecting it to cancer cell survival and clock period control.\",\n      \"evidence\": \"Co-IP, ubiquitination and stability assays, ligase screen, and circadian period measurement\",\n      \"pmids\": [\"30712944\", \"31607207\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Substrate motif on p21 and RevErb\\u03b1 not mapped\", \"Paralog redundancy (SPSB4) for RevErb\\u03b1 not fully separated functionally\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed SPSB1 restrains NF-\\u03baB at or downstream of the p65 heterodimer via its SOCS box, broadening its innate-immune brake function.\",\n      \"evidence\": \"Systematic SOCS-box siRNA screen, NF-\\u03baB reporters, endogenous Co-IP, and translocation imaging\",\n      \"pmids\": [\"32038638\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Whether p65 is a degradation substrate or sequestered partner unresolved\", \"Step downstream of nuclear translocation not pinpointed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established an in vivo pathological role: inflammatory cytokines induce SPSB1 to degrade T\\u03b2RII and drive sepsis muscle atrophy, reversible by knockdown.\",\n      \"evidence\": \"Co-IP, ubiquitination, half-life and protein synthesis assays, plus AAV9-shRNA in vivo rescue in septic mice\",\n      \"pmids\": [\"37209006\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Relative contribution of T\\u03b2RII degradation vs other substrates to atrophy not quantified\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Connected SPSB1 to tumor immune evasion, showing it degrades KLF6 to limit PD-L1 and is post-transcriptionally controlled by PTBP3.\",\n      \"evidence\": \"Knockdown, ubiquitination assay, T cell exhaustion co-culture, in vivo tumor models, and mRNA stability assay\",\n      \"pmids\": [\"42055144\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct vs indirect ubiquitination of KLF6 not biochemically isolated\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SPSB1 selects among its many substrates in a given cell context, and what governs whether it builds degradative versus non-degradative ubiquitin chains, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No unified model for context-dependent substrate prioritization\", \"Chain-linkage determinants for K29 vs canonical degradative chains undefined\", \"No structural model of the assembled SPSB1-Cullin-5-substrate ligase\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 3, 6, 7, 10, 11]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 8]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 3, 6, 7, 10, 11]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 4, 8, 10]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 9, 11]},\n      {\"term_id\": \"R-HSA-9909396\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [\"Elongin B/C-Cullin-5-Rbx2 E3 ligase\"],\n    \"partners\": [\"hnRNPA1\", \"NOS2\", \"TGFBR2\", \"MET\", \"CDKN1A\", \"NR1D1\", \"RELA\", \"KLF6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":6,"faith_total":6,"faith_pct":100.0}}