{"gene":"SMURF1","run_date":"2026-06-10T07:46:36","timeline":{"discoveries":[{"year":2001,"finding":"Smurf1 physically interacts with Smad7 and induces Smad7 ubiquitination and translocation from nucleus to cytoplasm; Smurf1 then associates with TGF-β type I receptor (TβR-I) via Smad7 as an adaptor, leading to enhanced proteasomal turnover of both TβR-I and Smad7.","method":"Co-immunoprecipitation, ubiquitination assays, overexpression in mammalian cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP and ubiquitination assays replicated across multiple subsequent studies; foundational mechanistic paper","pmids":["11278251"],"is_preprint":false},{"year":2002,"finding":"The C2 domain of Smurf1 is required to target the Smurf1-Smad7 complex to the plasma membrane; deletion of the C2 domain prevents plasma membrane localization, blocks recruitment of Smad7 to the TβR-II/TβR-I complex, and abolishes TβR-I ubiquitination and degradation as well as Smad7 inhibitory activity.","method":"C2-domain deletion mutant analysis, subcellular localization by microscopy, Co-IP, ubiquitination assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — domain deletion combined with localization, Co-IP, and functional ubiquitination assays in one study; independently supported by later C2-domain papers","pmids":["12151385"],"is_preprint":false},{"year":2003,"finding":"Smurf1 cooperates with inhibitory Smads (Smad6/7) to ubiquitinate and degrade BMP type I receptors; Smurf1 can also ubiquitinate Smad1/5 indirectly through I-Smads, expanding its inhibitory repertoire beyond direct Smad binding.","method":"Xenopus secondary axis assay, BMP-responsive reporter assay, ubiquitination assay, Co-IP","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods across two organisms; replicated by independent labs","pmids":["12857866"],"is_preprint":false},{"year":2003,"finding":"Smurf1 directly interacts with the osteoblast-specific transcription factor Runx2/Cbfa1 and mediates its ubiquitin- and proteasome-dependent degradation, controlling osteoblast differentiation.","method":"Co-IP, ubiquitination assay, proteasome inhibitor experiments, overexpression in osteoblast precursor cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding and ubiquitination demonstrated biochemically; replicated by multiple independent labs","pmids":["12738770"],"is_preprint":false},{"year":2003,"finding":"Increased Smurf1 expression promotes myogenic differentiation of C2C12 cells and blocks BMP-induced osteogenic conversion by selectively reducing endogenous Smad5 levels while leaving TGF-β-pathway Smads (Smad2, 3, 7) unaffected; siRNA-mediated depletion of endogenous Smurf1 is required for normal myogenic differentiation.","method":"Overexpression, siRNA knockdown, Western blot, Smad5 rescue experiment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain- and loss-of-function combined with rescue experiment; selectivity for Smad5 mechanistically defined","pmids":["12871975"],"is_preprint":false},{"year":2003,"finding":"Transgenic overexpression of Smurf1 in osteoblasts (under type I collagen promoter) significantly reduces bone formation in vivo, demonstrating a direct in vivo role for Smurf1 in suppressing osteoblast activity through BMP/Smad signaling components.","method":"Transgenic mouse generation, bone histomorphometry","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo transgenic model, single lab, no rescue experiment in this paper","pmids":["14701828"],"is_preprint":false},{"year":2005,"finding":"Smurf1-deficient mice develop age-dependent bone mass increase due to enhanced osteoblast activity; mechanistically, Smurf1 physically interacts with MEKK2 and promotes its ubiquitination and proteasomal degradation, thereby suppressing downstream JNK signaling in osteoblasts independently of canonical Smad-mediated BMP/TGF-β signaling.","method":"Smurf1-knockout mice, Co-IP, in vitro ubiquitination assay, JNK pathway analysis","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — genetic KO with phenotype, direct biochemical interaction and ubiquitination, pathway epistasis; published in Cell","pmids":["15820682"],"is_preprint":false},{"year":2005,"finding":"Smurf1 ubiquitinates RhoA and physically interacts with it in neuroblastoma cells; overexpression of Smurf1 selectively reduces RhoA protein levels during cAMP-induced (but not retinoic acid-induced) neurite outgrowth, promoting neurite extension.","method":"Co-IP, ubiquitination assay, proteasome inhibitor, Neuro2a neurite outgrowth assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical interaction and functional assay in single lab; extends established RhoA-Smurf1 mechanism to neurons","pmids":["15710384"],"is_preprint":false},{"year":2005,"finding":"TNF-α up-regulates Smurf1 and Smurf2 expression in osteoblasts and promotes proteasomal degradation of Runx2, an effect blocked by siRNA against Smurf1, establishing that TNF-mediated Runx2 degradation requires Smurf1.","method":"siRNA knockdown, Western blot, proteasome inhibitor, reporter assay, in vivo TNF transgenic mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro siRNA epistasis and in vivo TNF transgenic data converge; replicated in the 2008 follow-up study","pmids":["16373342"],"is_preprint":false},{"year":2006,"finding":"Using Smurf1-deficient cells and siRNA knockdown, Smurf1 is identified as a rate-limiting, specific factor for ubiquitin-mediated proteasomal degradation of activated (CNF1-constitutively active) RhoA; ectopic Smurf1 restores RhoA ubiquitylation in Smurf1-deficient Vero cells.","method":"Smurf1-KO cells, siRNA, CNF1 toxin treatment, ubiquitination assay, rescue by ectopic Smurf1","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO plus siRNA plus rescue experiment; direct mechanistic demonstration of Smurf1 as the specific E3 for active RhoA","pmids":["16540523"],"is_preprint":false},{"year":2006,"finding":"Smurf1-mediated RhoA degradation at the cell periphery reduces ROCK activity and myosin light chain 2 (MLC2) phosphorylation locally, enabling lamellipodia formation and 2D tumor cell motility; in 3D invasion, Smurf1 inhibition induces amoeboid-like transition and more invasive behavior.","method":"Smurf1 siRNA, ROCK activity assay, MLC2 phosphorylation, 2D and 3D invasion assays, in vivo tumor migration","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple assays (biochemical, 2D, 3D, in vivo) linking Smurf1-RhoA to ROCK/MLC2 in single study","pmids":["17190792"],"is_preprint":false},{"year":2006,"finding":"FKBP12 acts as an adaptor for the Smad7-Smurf1 complex on the activin type I receptor (ALK4); FK506, which dissociates FKBP12 from the receptor, decreases Smad7-Smurf1 interaction and inhibits TβR-I ubiquitination by Smurf1.","method":"Co-IP, ubiquitination assay, FK506 pharmacological interference","journal":"Journal of molecular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical interaction and pharmacological intervention, single lab","pmids":["16720724"],"is_preprint":false},{"year":2006,"finding":"LMP-1 interacts with the WW2 domain of Smurf1 via a PPxY-like motif and competes with Smad1/5 for Smurf1 binding, blocking ubiquitination of Smads and increasing BMP responsiveness.","method":"Co-IP, ubiquitination assay, competitive binding/peptide competition","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct competition and ubiquitination assays, single lab","pmids":["16611643"],"is_preprint":false},{"year":2006,"finding":"Smurf1 regulates neural patterning in Xenopus embryos by ubiquitin-mediated degradation of Smad1; morpholino-mediated Smurf1 knockdown elevates phospho-Smad1 levels in dorsal ectoderm and disrupts neural folding, placing Smurf1 as an antagonist of BMP/Smad1 signaling required for neural development.","method":"Antisense morpholino knockdown, dominant-negative protein, phospho-Smad1 Western blot, Xenopus embryology","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in Xenopus with biochemical readout, single lab","pmids":["16973150"],"is_preprint":false},{"year":2008,"finding":"Smurf2 interacts with Smurf1 and induces its ubiquitination and proteasomal degradation (but not vice versa), providing a post-translational mechanism for cross-regulation between these two related E3 ligases.","method":"Co-IP, ubiquitination assay, Western blot after Smurf2 knockdown","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical evidence in single lab with reciprocal experiments showing asymmetry","pmids":["18927080"],"is_preprint":false},{"year":2008,"finding":"CKIP-1 specifically interacts with the linker region between the WW domains of Smurf1 (not Smurf2) and augments Smurf1's E3 ligase activity and substrate affinity; CKIP-1-deficient mice show age-dependent bone mass increase due to reduced Smurf1 activity.","method":"Co-IP, in vitro ubiquitination assay, domain mapping, CKIP-1 knockout mouse","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro ubiquitination assay with domain mapping, KO mouse phenotype, multiple orthogonal methods in single rigorous study","pmids":["18641638"],"is_preprint":false},{"year":2008,"finding":"Smurf1 interacts with hPEM-2 (a GEF for Cdc42) via a Ca2+-independent C2 domain interaction (mapped to residues 318–343 of the PH domain of hPEM-2) and induces its proteasomal degradation.","method":"GST pull-down, pulse-chase labeling, proteasome inhibitor, domain mapping","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical interaction and degradation assays, domain-level mapping, single lab","pmids":["18208356"],"is_preprint":false},{"year":2009,"finding":"Talin head (generated by calpain cleavage of talin) binds Smurf1 more tightly than full-length talin and is ubiquitylated by Smurf1 leading to its degradation; Cdk5 phosphorylates talin head at Ser425, which inhibits Smurf1 binding and prevents its degradation, thereby stabilizing focal adhesions and supporting cell migration.","method":"Co-IP, in vitro ubiquitination assay, kinase assay, phospho-mimetic/phospho-resistant mutants, focal adhesion assays, cell migration assay","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — reconstitution-level biochemistry (kinase assay + ubiquitination + phospho-mutants) combined with functional migration readout; published in Nature Cell Biology","pmids":["19363486"],"is_preprint":false},{"year":2009,"finding":"Smurf1 interacts with TRAF4 via TRAF4's PY motifs and the second WW domain of Smurf1, promoting ubiquitination and degradation of TRAF4; Smurf1 can ubiquitinate all six TRAF family members and thereby attenuates NF-κB signaling.","method":"Yeast two-hybrid, Co-IP, ubiquitination assay, NF-κB reporter","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus Co-IP plus functional reporter, single lab","pmids":["19937093"],"is_preprint":false},{"year":2010,"finding":"Smurf1 interacts with JunB via its PY motif and targets JunB for ubiquitination and proteasomal degradation; Smurf1-deficient MSCs have elevated JunB, increased cyclin D1, and enhanced osteoblast differentiation, placing Smurf1-JunB in a pathway controlling MSC proliferation.","method":"Co-IP, ubiquitination assay, Smurf1-KO cells, JunB knockdown/rescue","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical methods plus KO cells plus rescue","pmids":["20200942"],"is_preprint":false},{"year":2011,"finding":"The C2 domain of Smurf1 is necessary and sufficient to bind RhoA and is required for RhoA ubiquitination; the C2 domain is dispensable for Smad1 ubiquitination, revealing a substrate-selective role of the C2 domain. Two key lysines (K28 and K85) in the C2 domain are critical for plasma membrane localization and robust RhoA-directed ligase activity.","method":"Domain deletion/point mutants, GST pull-down, ubiquitination assay, crystal structure of C2 domain, cell migration assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure + mutagenesis + in vitro ubiquitination assay + functional cell assay in single study","pmids":["21402695"],"is_preprint":false},{"year":2011,"finding":"The C2 domain of Smurf1 is necessary and sufficient to bind RhoA (and also Axin), while the C2-HECT autoinhibitory mechanism observed in Smurf2 does not operate in Smurf1; instead, Smurf1's C2 domain functions in substrate selection rather than autoinhibition.","method":"FRET, Co-IP, domain deletion mutants, ubiquitination assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical domain mapping, single lab, complements crystal structure paper","pmids":["21708152"],"is_preprint":false},{"year":2011,"finding":"Cdh1 (APC/C adaptor) promotes Smurf1 E3 ligase activity independently of APC/C E3 activity by disrupting an autoinhibitory Smurf1 homodimer; Cdh1 depletion reduces Smurf1 activity, leading to MEKK2 accumulation and JNK activation, which drives osteoblast differentiation.","method":"Co-IP, in vitro ubiquitination assay, siRNA, homodimer disruption assay, osteoblast differentiation readout","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical demonstration of homodimer disruption plus E3 activity assay plus signaling and differentiation phenotype","pmids":["22152476"],"is_preprint":false},{"year":2011,"finding":"The SCF(FBXL15) ubiquitin ligase complex targets Smurf1 for ubiquitination and proteasomal degradation; FBXL15 specifically recognizes the HECT domain N-lobe of Smurf1 and ubiquitinates it at K355/K357, thereby positively regulating BMP signaling.","method":"Co-IP, ubiquitination assay, domain mapping, siRNA knockdown in zebrafish, siRNA injection in rat bone","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — site-specific ubiquitination mapping plus multi-organism functional validation","pmids":["21572392"],"is_preprint":false},{"year":2011,"finding":"Smurf1 interacts with WFS1 (Wolfram syndrome protein) at the ER via the C-terminal luminal region of WFS1 (residues 667–700) and promotes its ubiquitination and proteasomal degradation; ER stress induces Smurf1 degradation and WFS1 up-regulation, suggesting feedback regulation.","method":"Co-IP, ubiquitination assay, domain mapping, siRNA, ER stress inducers","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical interaction and ubiquitination with domain mapping, single lab","pmids":["21454619"],"is_preprint":false},{"year":2011,"finding":"Smurf1 interacts with and ubiquitinates KLF2 for proteasomal degradation specifically in lung cancer H1299 cells, requiring Smurf1's catalytic activity; this represses KLF2 transcriptional activity and alters expression of downstream targets (CD62L, Wee1).","method":"Co-IP, ubiquitination assay, catalytic mutant, reporter assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical interaction and ubiquitination with functional readout, single lab","pmids":["21382345"],"is_preprint":false},{"year":2011,"finding":"PKA-dependent phosphorylation of Smurf1 at Thr306 switches its substrate preference: Thr306-phosphorylated Smurf1 preferentially degrades RhoA over Par6; preventing this phosphorylation reduces axon formation in hippocampal neurons and impairs cortical neuron polarization in vivo.","method":"PKA phosphorylation assay, phospho-mimetic/resistant mutants, in vitro ubiquitination, cultured neuron axon formation assay, in utero electroporation","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — kinase assay + ubiquitination + phospho-mutants + in vivo cortical polarization; multiple orthogonal methods","pmids":["21262463"],"is_preprint":false},{"year":2012,"finding":"Ndfip1 enhances Smurf1 self-ubiquitination and its interaction with MAVS, promoting MAVS ubiquitination and degradation; Ndfip1 knockdown elevates MAVS levels and enhances RIG-I-dependent antiviral signaling.","method":"Co-IP, ubiquitination assay, siRNA knockdown, IFN-β reporter, IRF-3 phosphorylation assay","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical interaction and functional signaling assays, single lab","pmids":["23087404"],"is_preprint":false},{"year":2012,"finding":"Smurf1 interacts with STAT1 through its WW domains and the PY motif of STAT1, catalyzing K48-linked polyubiquitination and proteasomal degradation of STAT1 independently of STAT1 phosphorylation; Smurf1 overexpression attenuates IFN-γ signaling and antiviral response, while knockdown enhances them.","method":"Co-IP, domain mapping, ubiquitination assay (K48-linkage), siRNA, IFN-γ reporter, antiviral assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — domain-level interaction mapping, linkage-specific ubiquitination assay, gain/loss-of-function with functional signaling readouts","pmids":["22474288"],"is_preprint":false},{"year":2012,"finding":"Deubiquitinase USP9X (FAM) interacts with Smurf1 via the second WW domain of Smurf1 and the C-terminus of USP9X, antagonizing Smurf1 autoubiquitination and protecting Smurf1 from self-degradation; USP9X depletion leads to Smurf1 down-regulation and impaired cell migration.","method":"Quantitative MS, Co-IP, domain mapping, ubiquitination assay, siRNA, migration assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — mass spectrometry interactomics validated by Co-IP and domain mapping plus functional migration readout","pmids":["23184937"],"is_preprint":false},{"year":2013,"finding":"Smurf1 ubiquitinates Axin via atypical K29-linked polyubiquitin chains (at K789 and K821) without inducing degradation; this modification disrupts Axin's interaction with LRP5/6 co-receptors and attenuates Wnt-stimulated LRP6 phosphorylation, thereby repressing Wnt/β-catenin signaling.","method":"Co-IP, in vitro ubiquitination assay, K29-linkage-specific analysis, site-directed mutagenesis, Wnt reporter, Smurf1-KO MEFs","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — linkage-specific ubiquitination with mutagenesis, functional reporter, KO fibroblasts; multiple orthogonal methods","pmids":["23959799"],"is_preprint":false},{"year":2013,"finding":"Smurf1 induces non-degradative ubiquitination of TRAF4 at K190, which is required for proper localization of TRAF4 to tight junctions in confluent epithelial cells; this ubiquitination event is essential for TRAF4-mediated Rac1 activation and breast epithelial/cancer cell migration.","method":"Co-IP, ubiquitination assay with K190R mutant, localization by microscopy, Rac1 activation assay, migration assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — site-specific ubiquitination with functional mutant rescue, localization assay, Rac1 GEF activity, and migration phenotype","pmids":["23760265"],"is_preprint":false},{"year":2013,"finding":"Smurf1 directly interacts with and ubiquitinates TRIB2 (at a N-terminal domain, residues 1–5), a process requiring prior p70S6K-mediated phosphorylation of TRIB2 at Ser83; reduced p70S6K and Smurf1 in liver cancer leads to increased TRIB2 stability.","method":"Co-IP, ubiquitination assay, domain mapping, phospho-mutant analysis, half-life assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct interaction and ubiquitination with domain and phospho-mutant mapping, single lab","pmids":["24089522"],"is_preprint":false},{"year":2013,"finding":"PKA-mediated phosphorylation of Smurf1 at Thr306 prevents JNK-triggered Nur77 degradation by enabling unconventional (non-degradative) ubiquitination of Nur77 by Smurf1, resulting in Nur77 accumulation and mitochondrial translocation to induce apoptosis in cisplatin-treated cells.","method":"PKA phosphorylation assay, ubiquitination assay, Nur77 stability assay, apoptosis readout, phospho-mimetic mutants","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical kinase and ubiquitination assays with functional apoptosis readout, single lab","pmids":["23584473"],"is_preprint":false},{"year":2014,"finding":"Smurf1 is activated by neddylation: Smurf1 physically interacts with Nedd8 and Ubc12, forms a Nedd8-thioester intermediate, and auto-neddylates itself on multiple lysines via an active site at C426 in the HECT N-lobe; neddylation of Smurf1 enhances ubiquitin E2 recruitment and ubiquitin ligase activity. This regulatory mechanism is conserved in yeast Rsp5.","method":"In vitro neddylation assay, Nedd8-thioester intermediate detection, active-site mutagenesis (C426), yeast Rsp5 conservation test, ubiquitin E2 recruitment assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro neddylation, active-site mutagenesis, mechanistic thioester intermediate trapping, evolutionary conservation","pmids":["24821572"],"is_preprint":false},{"year":2014,"finding":"DNA damage (UV or MMS) activates ATR/Chk1, which phosphorylates Smurf1, enhancing Smurf1 self-degradation; this leads to RhoB accumulation and apoptosis. In the basal state, Smurf1 targets RhoB for degradation to control its abundance.","method":"Kinase assay, Smurf1 phospho-mutants, ubiquitination assay, apoptosis assay, Smurf1 overexpression/KD","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — ATR/Chk1/Smurf1 pathway defined by biochemical kinase assay and phospho-mutants with functional cell fate readout","pmids":["25249323"],"is_preprint":false},{"year":2014,"finding":"The C2 domain of Smurf1 mediates its interaction with Axin in a non-canonical manner (independent of WW-PY interaction); plasma membrane localization via the C2 domain is required for Axin ubiquitination. Smurf1-Axin interaction and K29-linked ubiquitination are attenuated in G2/M phase, correlating with increased Wnt responsiveness at that cell cycle stage.","method":"Co-IP, domain mapping, ubiquitination assay, cell cycle synchronization, Wnt reporter","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain mapping and cell cycle correlation, single lab building on prior Axin finding","pmids":["24700460"],"is_preprint":false},{"year":2016,"finding":"Smurf1 is required for selective autophagy of Mycobacterium tuberculosis (Mtb) in macrophages; Smurf1-/- macrophages fail to recruit polyubiquitin, NBR1, LC3, and LAMP1 to Mtb-associated structures. This function requires both the ubiquitin-ligase and C2 phospholipid-binding domains and involves K48-linked ubiquitination. Smurf1-/- mice show increased bacterial load and accelerated mortality.","method":"Smurf1-/- macrophages, domain mutant analysis, K48/K63-linkage ubiquitination assay, confocal microscopy for autophagy markers, in vivo mouse infection","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with in vivo infection, domain dissection, linkage-specific ubiquitination, multiple autophagy markers","pmids":["28017659"],"is_preprint":false},{"year":2016,"finding":"AMPK-mediated phosphorylation of Smurf1 at Ser148 controls osteoblast differentiation: a S148A knock-in mutation (preventing AMPK phosphorylation) causes premature osteoblast differentiation phenotype equivalent to Smurf1-/-, high bone mass, and hyperinsulinemia/hypoglycemia through increased Runx2 accumulation and elevated insulin receptor levels (Smurf1 also targets the insulin receptor for degradation).","method":"Smurf1 S148 knock-in mouse, Runx2 protein levels, insulin receptor degradation assay, phosphorylation by AMPK","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knock-in mouse with precise phospho-site and multiple downstream readouts","pmids":["27052174"],"is_preprint":false},{"year":2016,"finding":"Smurf1 deletion protects mice from pulmonary arterial hypertension; SMURF1 is identified as a key miR-140-5p target in PASMCs; SMURF1 knockdown alters BMP signaling in smooth muscle cells.","method":"Smurf1-/- mouse PAH model, miR-140-5p mimic delivery, SMURF1 siRNA, BMP signaling reporter","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO mouse and RNAi in disease model; mechanism via BMP signaling regulation","pmids":["27214554"],"is_preprint":false},{"year":2017,"finding":"Smurf1 interacts with Kindlin-2 and promotes its ubiquitination and degradation, thereby inhibiting αIIbβ3 and β1 integrin activation; Smurf1-KO MEFs show enhanced β1 integrin activation correlated with increased Kindlin-2 protein levels. Smurf1 selectively degrades Kindlin-2 but not Talin.","method":"Co-IP, ubiquitination assay, integrin activation assay, Smurf1-KO MEFs, colon cancer tissue correlation","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO cells plus biochemical ubiquitination plus functional integrin assay plus substrate selectivity demonstration","pmids":["28408404"],"is_preprint":false},{"year":2017,"finding":"Smurf1 directly interacts with PIPKIγ via its C2 domain and ubiquitinates PIPKIγ at K255, targeting it for degradation; PKA-mediated phosphorylation of Smurf1 at Thr306 (or Smurf1-T306D phospho-mimetic) prevents PIPKIγ degradation, linking PKA-Smurf1 signaling to lung cancer cell growth.","method":"Co-IP, ubiquitination assay, domain mapping, phospho-mimetic mutants, in vitro kinase assay, tumor growth assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical interaction, ubiquitination site mapping, phospho-mutant analysis, single lab","pmids":["28581524"],"is_preprint":false},{"year":2018,"finding":"SMURF1 interacts with ERα via its HECT domain and inhibits K48-specific polyubiquitination of ERα, stabilizing ERα protein and promoting ERα-dependent transcription and breast cancer cell proliferation.","method":"Co-IP with domain mapping, ubiquitin immunoprecipitation (K48-specific), protein stability assay, ERα reporter, siRNA, xenograft","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct interaction mapped to HECT domain, K48-ubiquitination assay, functional reporter and cell/xenograft phenotype, single lab","pmids":["29433542"],"is_preprint":false},{"year":2018,"finding":"Smurf1 mediates non-proteolytic K63-linked ubiquitination of PPARγ, suppressing its transcriptional activity; Smurf1-deficient mice develop spontaneous hepatic steatosis with up-regulated PPARγ target genes, and PPARγ antagonist treatment fully reverses lipid accumulation.","method":"Smurf1-KO mouse, K63-linkage-specific ubiquitination assay, PPARγ reporter, PPARγ antagonist rescue, high-fat diet experiment","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — genetic KO mouse, linkage-specific ubiquitination, pharmacological rescue; multiple orthogonal methods","pmids":["30566427"],"is_preprint":false},{"year":2018,"finding":"SMURF1 is expressed at the primary cilium and at the outflow tract cushion mesenchyme during heart development; Smurf1-/- embryos show delayed outflow tract septation and reduced aortic smooth muscle layer thickness; Smurf1 promotes smooth muscle and cardiac fibroblast differentiation while negatively regulating cardiomyogenesis.","method":"Smurf1-/- mouse embryos, immunofluorescence localization to primary cilium, histomorphometry, differentiation marker analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse phenotype plus localization to cilium; differentiation assays, single lab","pmids":["29934521"],"is_preprint":false},{"year":2018,"finding":"CKIP-1 and Smurf1 are co-expressed at the chick neural plate border; CKIP-1 knockdown causes neural crest loss by suppressing BMP/pSmad1/5/8 signaling; Smurf1 overexpression mimics CKIP-1 loss (both reduce pSmad1/5/8); epistasis shows CKIP-1 rescues Smurf1-mediated neural crest loss by suppressing Smurf1-mediated Smad degradation.","method":"Morpholino knockdown, Smurf1 overexpression, BMP reporter, pSmad1/5/8 Western blot, epistasis (CKIP-1 rescue of Smurf1 OE)","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple pathway readouts, in vivo chick model","pmids":["29949573"],"is_preprint":false},{"year":2019,"finding":"SMURF1 ubiquitinates UVRAG at K517 and K559 via K29/K33-linked polyubiquitin chains, reducing UVRAG-RUBCN association and promoting autophagosome maturation; CSNK1A1-mediated phosphorylation of UVRAG at Ser522 blocks SMURF1 binding to UVRAG; deubiquitinase ZRANB1 removes SMURF1-catalyzed chains from UVRAG, restoring RUBCN binding.","method":"Co-IP, in vitro ubiquitination assay, site-directed mutagenesis, autophagosome maturation assay, kinase assay, deubiquitinase assay","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — site-specific ubiquitination, linkage determination, phospho-mutant regulation, orthogonal DUB and kinase assays, in vitro and in vivo evidence","pmids":["30686098"],"is_preprint":false},{"year":2019,"finding":"SMURF1 interacts with and ubiquitinates ARHGAP26, a negative regulator of RhoA (RhoA-GAP), promoting its degradation and thereby sustaining RhoA-GTP levels, which activates β-catenin signaling and promotes ovarian cancer cell invasion and migration.","method":"Co-IP, ubiquitination assay, ARHGAP26 overexpression/knockdown, RhoA-GTP pull-down, in vivo lung metastasis assay","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct interaction and ubiquitination assay with functional rescue, single lab","pmids":["31004081"],"is_preprint":false},{"year":2020,"finding":"Smurf1 ubiquitylates and degrades PTEN, leading to PI3K/Akt/mTOR pathway activation; Smurf1-deficient glioblastoma cells have restored PTEN activity, reduced PI3K/Akt signaling, and are sensitized to rapamycin; combined Smurf1 knockdown plus rapamycin reduces tumor progression in an orthotopic GBM model.","method":"Co-IP, ubiquitination assay, PTEN activity assay, Smurf1 siRNA, in vivo orthotopic GBM model, rapamycin combination","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct ubiquitination and functional tumor model, single lab","pmids":["32737433"],"is_preprint":false},{"year":2021,"finding":"Smurf1 acts as a Nedd8 ligase (in addition to ubiquitin ligase) to catalyze neddylation of RRP9 (U3 snoRNP component) primarily at K221; RRP9 neddylation promotes pre-rRNA processing and ribosome biogenesis; unneddylated RRP9-K221R lacks tumor-promoting activity. NEDP1 removes Nedd8 from RRP9.","method":"In vivo and in vitro neddylation assay, site-directed mutagenesis (K221R), pre-rRNA processing assay, co-IP, functional tumor proliferation/migration assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro neddylation, site mapping by mutagenesis, deneddylase identification, functional ribosome biogenesis assay","pmids":["34662580"],"is_preprint":false},{"year":2021,"finding":"SMURF1 ubiquitylates and degrades SHP-1 (a protein tyrosine phosphatase), activating STAT3 signaling; SMURF1 and SHP-1 protein levels are inversely correlated in endometriosis tissue, and SMURF1-mediated SHP-1 degradation promotes endometrial stromal cell proliferation and invasion.","method":"Co-IP, ubiquitination assay, Co-IP in patient tissues, siRNA/overexpression, STAT3 activation assay, invasion assay","journal":"Annals of translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical interaction/ubiquitination with functional cellular readout, single lab","pmids":["33842583"],"is_preprint":false},{"year":2022,"finding":"ERK phosphorylates Smurf1 at Thr223 upon TGFβ stimulation; this phosphorylation is a prerequisite for Smurf1-mediated RhoA polyubiquitination and degradation, cytoskeletal rearrangement, and EMT; blocking Thr223 phosphorylation inhibits TGFβ-induced EMT and dramatically reduces lung metastasis of murine breast cancer in vivo.","method":"Kinase assay, phospho-mutants, Co-IP, ubiquitination assay, EMT markers, in vivo lung metastasis","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 2 / Strong — kinase phosphorylation site identified and functionally validated with phospho-mutants in vitro and in vivo metastasis model","pmids":["35654587"],"is_preprint":false},{"year":2023,"finding":"Smurf1 interacts with the TGR5 intracellular loop 2 (ICL2) region via its HECT domain and mediates K11/K48-linked polyubiquitination of TGR5 at K306, leading to proteasomal degradation of TGR5 under high glucose stimulation; genetic Smurf1 deficiency restores TGR5 and attenuates renal injury in diabetic mice.","method":"Co-IP, domain mapping, site-directed mutagenesis (K306R), K11/K48-linkage-specific ubiquitination assay, Smurf1-KO diabetic mouse model","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — site-specific ubiquitination with domain mapping and mutagenesis, linkage determination, and KO mouse phenotype","pmids":["37481723"],"is_preprint":false},{"year":2024,"finding":"Smurf1 triggers PDK1 neddylation upon growth factor stimulation; poly-Nedd8 chains on PDK1 recruit methyltransferase SETDB1 to form a cytoplasmic complex (cCOMPASS: PDK1-Smurf1-SETDB1) that directs Akt membrane attachment and T308 phosphorylation; Smurf1 deficiency reduces CRC tumorigenesis; a Smurf1-specific degrader (SART-1) blocks PDK1-Akt signaling and suppresses KRAS-mutated CRC tumors.","method":"In vitro neddylation assay, Co-IP, Smurf1 genetic KO in CRC mouse model, Akt membrane recruitment assay, Smurf1 PROTAC degrader, PDK1 inhibitor combination","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — reconstituted neddylation, complex identification, genetic KO mouse model, pharmacological degrader with mechanism validation","pmids":["39039255"],"is_preprint":false}],"current_model":"SMURF1 is a HECT-domain E3 ubiquitin ligase (and Nedd8 ligase) that uses its C2 domain for membrane targeting and substrate selection, its WW domains for PY-motif-containing substrates, and its HECT domain for catalysis; it is activated by neddylation (auto-catalyzed via C426) and by co-factors CKIP-1 and Cdh1, regulated by PKA/Chk1/ERK/AMPK/IRAK2-mediated phosphorylation that can switch substrate preference (e.g., RhoA vs. Par6) or trigger self-degradation, and it ubiquitinates a broad set of substrates—including Smad1/5, Runx2, RhoA, RhoB, MEKK2, TGF-β/BMP receptors (via Smad7), MAVS, STAT1, talin head, Kindlin-2, TRAF proteins, JunB, Axin (K29-linked, non-degradative), PPARγ (K63-linked, non-degradative), UVRAG, PTEN, TGR5, and PDK1 (neddylation)—thereby controlling BMP/TGF-β signaling, osteoblast differentiation, Wnt/β-catenin signaling, cell polarity and migration, autophagy, antiviral immunity, metabolic homeostasis, and PI3K-Akt-driven tumorigenesis."},"narrative":{"mechanistic_narrative":"SMURF1 is a HECT-domain E3 ubiquitin ligase that governs cellular responses to the BMP/TGF-β family, cell polarity and migration, and several metabolic and immune programs by selectively ubiquitinating signaling proteins [PMID:11278251, PMID:15820682]. Its founding activity is the negative regulation of TGF-β/BMP signaling: SMURF1 binds the inhibitory Smad7, ubiquitinates it, and uses it as an adaptor to recruit and degrade the type I receptor, and it cooperates with inhibitory Smads to degrade BMP receptors and Smad1/5, thereby antagonizing osteoblastic differentiation and patterning [PMID:11278251, PMID:12857866, PMID:12871975]. A C2 domain provides membrane targeting and substrate selection — it is required to localize the SMURF1–Smad7 complex to the plasma membrane and is necessary and sufficient to bind substrates such as RhoA and Axin, while the WW domains capture PY-motif substrates and the HECT domain catalyzes transfer [PMID:12151385, PMID:21402695, PMID:21708152]. SMURF1 controls cell motility by degrading active RhoA locally to limit ROCK/MLC2 signaling and enable lamellipodial protrusion [PMID:16540523, PMID:17190792], and it shapes adhesion through degradation of talin head and Kindlin-2 [PMID:19363486, PMID:28408404]. Beyond canonical degradative ubiquitination, SMURF1 installs non-proteolytic chains: K29-linked ubiquitination of Axin disrupts LRP6 coupling to repress Wnt/β-catenin signaling, K63-linked ubiquitination of PPARγ suppresses its transcription to restrain hepatic lipid accumulation, and K29/K33-linked ubiquitination of UVRAG promotes autophagosome maturation [PMID:23959799, PMID:30566427, PMID:30686098]. SMURF1 is also required for selective autophagy of intracellular Mycobacterium tuberculosis and attenuates antiviral and cytokine signaling by degrading MAVS and STAT1 [PMID:28017659, PMID:23087404, PMID:22474288]. The enzyme is auto-activated by neddylation through an active-site cysteine (C426), and additionally acts as a Nedd8 ligase toward substrates: it neddylates RRP9 to promote ribosome biogenesis and neddylates PDK1 to assemble a cytoplasmic PDK1–SMURF1–SETDB1 complex driving Akt activation and KRAS-mutant tumorigenesis [PMID:24821572, PMID:34662580, PMID:39039255]. SMURF1 activity is tuned by co-factors (CKIP-1, Cdh1) and by kinase inputs — PKA phosphorylation at Thr306, ERK at Thr223, AMPK at Ser148, and ATR/Chk1 — that switch substrate preference or trigger self-degradation [PMID:18641638, PMID:22152476, PMID:21262463, PMID:35654587, PMID:27052174, PMID:25249323].","teleology":[{"year":2001,"claim":"Established the founding function of SMURF1 as a negative regulator of TGF-β signaling by showing it ubiquitinates Smad7 and uses it to target the type I receptor.","evidence":"Co-IP and ubiquitination assays in mammalian cells","pmids":["11278251"],"confidence":"High","gaps":["Did not define the ubiquitin chain linkage","Did not address regulation of SMURF1 activity itself"]},{"year":2002,"claim":"Identified the C2 domain as the membrane-targeting module required for receptor recruitment, answering how the ligase reaches its membrane substrates.","evidence":"C2-deletion mutants with localization, Co-IP, and ubiquitination assays","pmids":["12151385"],"confidence":"High","gaps":["Structural basis of C2 membrane/substrate binding not resolved here","Did not test C2 role for non-receptor substrates"]},{"year":2003,"claim":"Extended the inhibitory repertoire to BMP receptors and the osteoblast transcription factor Runx2, placing SMURF1 at the center of bone/skeletal differentiation control.","evidence":"Xenopus axis and reporter assays, Co-IP and ubiquitination in osteoblast precursors, Smad5-selective degradation with rescue","pmids":["12857866","12738770","12871975"],"confidence":"High","gaps":["Selectivity determinants distinguishing Smad5 from Smad2/3 not mapped","In vivo bone consequence not yet shown in these reports"]},{"year":2005,"claim":"Genetic loss-of-function defined SMURF1 as a physiological suppressor of osteoblast activity and revealed a Smad-independent axis through MEKK2/JNK.","evidence":"Smurf1-knockout mice with bone phenotype, Co-IP, in vitro ubiquitination, and JNK epistasis; RhoA degradation shown in neurons","pmids":["15820682","15710384"],"confidence":"High","gaps":["How SMURF1 partitions between Smad and MEKK2 substrates in vivo unclear","Upstream signals selecting MEKK2 not defined"]},{"year":2006,"claim":"Defined SMURF1 as the rate-limiting, specific E3 for activated RhoA and linked this to localized cytoskeletal control of migration and invasion.","evidence":"Smurf1-KO cells with rescue, CNF1 activation, ROCK/MLC2 readouts, 2D/3D invasion and in vivo migration assays","pmids":["16540523","17190792"],"confidence":"High","gaps":["Spatial mechanism restricting RhoA degradation to the cell periphery not fully resolved","Determinants of active- versus inactive-RhoA recognition unclear"]},{"year":2008,"claim":"Identified co-factor and cross-regulatory control of SMURF1 activity, showing CKIP-1 augments its ligase activity and Smurf2 degrades it.","evidence":"Co-IP, domain mapping, in vitro ubiquitination, and CKIP-1 knockout mouse bone phenotype","pmids":["18641638","18927080"],"confidence":"High","gaps":["Mechanism by which CKIP-1 increases catalytic output not structurally defined","Physiological trigger for Smurf2-mediated SMURF1 turnover unknown"]},{"year":2009,"claim":"Showed SMURF1 controls focal-adhesion turnover by degrading the calpain-generated talin head, and that Cdk5 phosphorylation of talin protects it, integrating proteolysis into adhesion dynamics.","evidence":"Co-IP, in vitro ubiquitination, kinase assay, phospho-mutants, focal adhesion and migration assays","pmids":["19363486"],"confidence":"High","gaps":["Whether full-length talin is ever a substrate in vivo unclear","Coordination with RhoA-directed activity during migration not addressed"]},{"year":2011,"claim":"Provided structural and mechanistic dissection: the C2 domain mediates substrate selection (RhoA, Axin) rather than Smurf2-type autoinhibition, and Cdh1 activates SMURF1 by disrupting an autoinhibitory homodimer.","evidence":"C2 crystal structure with mutagenesis, FRET, ubiquitination assays, and Cdh1 homodimer-disruption and osteoblast differentiation readouts; SCF(FBXL15) shown to degrade SMURF1","pmids":["21402695","21708152","22152476","21572392"],"confidence":"High","gaps":["Full-length SMURF1 structure and chain-type determinants not resolved","How Cdh1 and CKIP-1 inputs are integrated unclear"]},{"year":2011,"claim":"Revealed PKA phosphorylation at Thr306 as a substrate-preference switch directing SMURF1 toward RhoA over Par6 to control neuronal polarization.","evidence":"PKA kinase assay, phospho-mutants, in vitro ubiquitination, neuronal axon-formation assay, in utero electroporation","pmids":["21262463"],"confidence":"High","gaps":["Structural basis of phospho-driven substrate switching not defined","Other kinases acting at the same site not yet identified"]},{"year":2012,"claim":"Connected SMURF1 to antiviral and cytokine signaling by degrading MAVS (with Ndfip1) and K48-ubiquitinating STAT1, and identified USP9X as a stabilizing deubiquitinase.","evidence":"Co-IP, linkage-specific ubiquitination, siRNA, IFN reporters, and mass-spectrometry interactomics","pmids":["23087404","22474288","23184937"],"confidence":"High","gaps":["In vivo immune phenotypes of these substrate relationships not established here","Balance between USP9X protection and Smurf2/FBXL15 turnover unclear"]},{"year":2013,"claim":"Demonstrated that SMURF1 builds non-degradative ubiquitin chains — K29-linked on Axin to repress Wnt and K190 on TRAF4 for localization — expanding its output beyond proteasomal degradation.","evidence":"Linkage-specific and site-specific ubiquitination assays, mutagenesis, Wnt reporters, Smurf1-KO MEFs, Rac1 activation and migration assays","pmids":["23959799","23760265"],"confidence":"High","gaps":["How SMURF1 selects chain linkage per substrate is unknown","Readers decoding the K29 Axin chain not identified"]},{"year":2014,"claim":"Identified neddylation as a core regulatory mechanism: SMURF1 auto-neddylates via C426 to boost E2 recruitment and ligase activity, and DNA-damage Chk1 signaling drives SMURF1 self-degradation to permit RhoB-dependent apoptosis.","evidence":"Reconstituted in vitro neddylation, thioester trapping, active-site mutagenesis, yeast Rsp5 conservation; kinase assays and phospho-mutants for the Chk1 axis","pmids":["24821572","25249323"],"confidence":"High","gaps":["Endogenous triggers of SMURF1 auto-neddylation in cells not defined","Phospho-sites mediating Chk1-driven self-degradation not fully mapped"]},{"year":2016,"claim":"Established SMURF1 as a mediator of selective xenophagy and an AMPK-controlled metabolic node, requiring its C2 and ligase domains for anti-mycobacterial autophagy and Ser148 phosphorylation for osteoblast/insulin-receptor control.","evidence":"Smurf1-/- macrophages and infection in mice, domain and linkage analysis; Smurf1 S148A knock-in mouse with bone and glucose phenotypes","pmids":["28017659","27052174"],"confidence":"High","gaps":["Direct ubiquitinated cargo on Mtb-associated structures not fully defined","How AMPK phosphorylation alters catalytic behavior mechanistically unclear"]},{"year":2018,"claim":"Defined a metabolic role through non-degradative K63 ubiquitination of PPARγ, with Smurf1 loss causing hepatic steatosis reversible by PPARγ antagonism.","evidence":"Smurf1-KO mouse, K63-linkage-specific ubiquitination, PPARγ reporter, pharmacological rescue, high-fat diet","pmids":["30566427"],"confidence":"High","gaps":["Tissue-specific contribution of SMURF1 to lipid metabolism not dissected","Coordination with other PPARγ regulators unknown"]},{"year":2019,"claim":"Showed SMURF1 promotes autophagosome maturation by K29/K33-ubiquitinating UVRAG, with kinase and DUB inputs (CSNK1A1, ZRANB1) gating the modification.","evidence":"Co-IP, site-specific and linkage-determined ubiquitination, autophagosome maturation, kinase and deubiquitinase assays","pmids":["30686098"],"confidence":"High","gaps":["How UVRAG ubiquitination integrates with the xenophagy role unclear","Structural recognition of UVRAG sites not resolved"]},{"year":2021,"claim":"Expanded SMURF1 to a bona fide Nedd8 ligase by showing it neddylates RRP9 to promote pre-rRNA processing and ribosome biogenesis.","evidence":"In vivo/in vitro neddylation, K221R mutagenesis, pre-rRNA processing assay, NEDP1 deneddylation, tumor proliferation assays","pmids":["34662580"],"confidence":"High","gaps":["Determinants distinguishing ubiquitin versus Nedd8 transfer not defined","Scope of the SMURF1 neddylome unknown"]},{"year":2022,"claim":"Identified ERK phosphorylation at Thr223 as a TGFβ-induced prerequisite for RhoA degradation, EMT, and metastasis, providing a druggable kinase–ligase link.","evidence":"Kinase assay, phospho-mutants, Co-IP, ubiquitination, EMT markers, in vivo lung metastasis","pmids":["35654587"],"confidence":"High","gaps":["Interplay between Thr223 (ERK) and Thr306 (PKA) phospho-control not resolved","Whether other migration substrates respond to Thr223 status unknown"]},{"year":2024,"claim":"Linked SMURF1 neddylase activity to oncogenic Akt signaling: PDK1 neddylation assembles a cytoplasmic PDK1–SMURF1–SETDB1 complex driving Akt activation, and a SMURF1 degrader suppresses KRAS-mutant tumors.","evidence":"In vitro neddylation, complex identification, Smurf1-KO CRC mouse model, Akt membrane-recruitment assay, PROTAC degrader","pmids":["39039255"],"confidence":"High","gaps":["How SETDB1 methyltransferase activity contributes mechanistically unclear","Selectivity and broader effects of the degrader not fully characterized"]},{"year":null,"claim":"It remains unresolved how SMURF1 selects between proteasomal versus non-degradative chain linkages and between ubiquitin versus Nedd8 transfer for a given substrate, and how its many kinase and co-factor inputs are integrated on a single full-length enzyme.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No full-length structure capturing substrate, co-factor, and chain-type selection","No unified model reconciling competing phospho-inputs (PKA/ERK/AMPK/Chk1)","Determinants of ubiquitin-versus-Nedd8 cofactor choice undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3,6,9,28,40]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,34,49]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1,20,37]},{"term_id":"GO:0031386","term_label":"protein tag activity","supporting_discovery_ids":[34,49,53]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,10,20,36]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,53]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[44]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,6,30]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[37,46]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[27,28]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[38,43]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,5,6,13,44]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,3,34]}],"complexes":["PDK1-SMURF1-SETDB1 (cCOMPASS)"],"partners":["SMAD7","RHOA","AXIN1","CKIP-1","MEKK2","USP9X","UVRAG","TRAF4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9HCE7","full_name":"E3 ubiquitin-protein ligase SMURF1","aliases":["HECT-type E3 ubiquitin transferase SMURF1","SMAD ubiquitination regulatory factor 1","SMAD-specific E3 ubiquitin-protein ligase 1"],"length_aa":757,"mass_kda":86.1,"function":"E3 ubiquitin-protein ligase that acts as a negative regulator of BMP signaling pathway. Mediates ubiquitination and degradation of SMAD1 and SMAD5, 2 receptor-regulated SMADs specific for the BMP pathway. Promotes ubiquitination and subsequent proteasomal degradation of TRAF family members and RHOA. Promotes ubiquitination and subsequent proteasomal degradation of MAVS (PubMed:23087404). Acts as an antagonist of TGF-beta signaling by ubiquitinating TGFBR1 and targeting it for degradation (PubMed:21791611). Plays a role in dendrite formation by melanocytes (PubMed:23999003)","subcellular_location":"Cytoplasm; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9HCE7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SMURF1","classification":"Not Classified","n_dependent_lines":26,"n_total_lines":1208,"dependency_fraction":0.02152317880794702},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SMURF1","total_profiled":1310},"omim":[{"mim_id":"608580","title":"MYOSIN, HEAVY CHAIN 16, SKELETAL MUSCLE, PSEUDOGENE; MYH16","url":"https://www.omim.org/entry/608580"},{"mim_id":"607929","title":"CCM2 SCAFFOLD PROTEIN; CCM2","url":"https://www.omim.org/entry/607929"},{"mim_id":"607484","title":"PAR6 FAMILY CELL POLARITY REGULATOR ALPHA; PARD6A","url":"https://www.omim.org/entry/607484"},{"mim_id":"605568","title":"SMAD-SPECIFIC E3 UBIQUITIN PROTEIN LIGASE 1; SMURF1","url":"https://www.omim.org/entry/605568"},{"mim_id":"605532","title":"SMAD-SPECIFIC E3 UBIQUITIN PROTEIN LIGASE 2; SMURF2","url":"https://www.omim.org/entry/605532"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SMURF1"},"hgnc":{"alias_symbol":["KIAA1625"],"prev_symbol":[]},"alphafold":{"accession":"Q9HCE7","domains":[{"cath_id":"2.60.40.150","chopping":"12-138","consensus_level":"high","plddt":84.9409,"start":12,"end":138},{"cath_id":"3.90.1750.10","chopping":"373-634","consensus_level":"medium","plddt":86.2324,"start":373,"end":634},{"cath_id":"3.30.2410.10","chopping":"639-749","consensus_level":"high","plddt":88.4318,"start":639,"end":749}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HCE7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HCE7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HCE7-F1-predicted_aligned_error_v6.png","plddt_mean":73.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SMURF1","jax_strain_url":"https://www.jax.org/strain/search?query=SMURF1"},"sequence":{"accession":"Q9HCE7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9HCE7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9HCE7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HCE7"}},"corpus_meta":[{"pmid":"11278251","id":"PMC_11278251","title":"Smurf1 interacts with transforming growth factor-beta type I receptor through Smad7 and induces receptor degradation.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11278251","citation_count":707,"is_preprint":false},{"pmid":"15820682","id":"PMC_15820682","title":"Ubiquitin ligase Smurf1 controls osteoblast activity and bone homeostasis by targeting MEKK2 for degradation.","date":"2005","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/15820682","citation_count":311,"is_preprint":false},{"pmid":"12857866","id":"PMC_12857866","title":"Cooperative inhibition of bone morphogenetic protein signaling by Smurf1 and inhibitory Smads.","date":"2003","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/12857866","citation_count":266,"is_preprint":false},{"pmid":"16373342","id":"PMC_16373342","title":"Tumor necrosis factor promotes Runx2 degradation through up-regulation of Smurf1 and Smurf2 in osteoblasts.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16373342","citation_count":265,"is_preprint":false},{"pmid":"12738770","id":"PMC_12738770","title":"E3 ubiquitin ligase Smurf1 mediates core-binding factor alpha1/Runx2 degradation and plays a specific role in osteoblast differentiation.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12738770","citation_count":244,"is_preprint":false},{"pmid":"24821572","id":"PMC_24821572","title":"The covalent modifier Nedd8 is critical for the activation of Smurf1 ubiquitin ligase in tumorigenesis.","date":"2014","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/24821572","citation_count":186,"is_preprint":false},{"pmid":"28017659","id":"PMC_28017659","title":"The Ubiquitin Ligase Smurf1 Functions in Selective Autophagy of Mycobacterium tuberculosis and Anti-tuberculous Host Defense.","date":"2016","source":"Cell 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signalling","url":"https://pubmed.ncbi.nlm.nih.gov/29753111","citation_count":19,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":52045,"output_tokens":12973,"usd":0.175365,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":24305,"output_tokens":6324,"usd":0.139813,"stage2_stop_reason":"end_turn"},"total_usd":0.315178,"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\": 2001,\n      \"finding\": \"Smurf1 physically interacts with Smad7 and induces Smad7 ubiquitination and translocation from nucleus to cytoplasm; Smurf1 then associates with TGF-β type I receptor (TβR-I) via Smad7 as an adaptor, leading to enhanced proteasomal turnover of both TβR-I and Smad7.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, overexpression in mammalian cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP and ubiquitination assays replicated across multiple subsequent studies; foundational mechanistic paper\",\n      \"pmids\": [\"11278251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The C2 domain of Smurf1 is required to target the Smurf1-Smad7 complex to the plasma membrane; deletion of the C2 domain prevents plasma membrane localization, blocks recruitment of Smad7 to the TβR-II/TβR-I complex, and abolishes TβR-I ubiquitination and degradation as well as Smad7 inhibitory activity.\",\n      \"method\": \"C2-domain deletion mutant analysis, subcellular localization by microscopy, Co-IP, ubiquitination assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — domain deletion combined with localization, Co-IP, and functional ubiquitination assays in one study; independently supported by later C2-domain papers\",\n      \"pmids\": [\"12151385\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Smurf1 cooperates with inhibitory Smads (Smad6/7) to ubiquitinate and degrade BMP type I receptors; Smurf1 can also ubiquitinate Smad1/5 indirectly through I-Smads, expanding its inhibitory repertoire beyond direct Smad binding.\",\n      \"method\": \"Xenopus secondary axis assay, BMP-responsive reporter assay, ubiquitination assay, Co-IP\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods across two organisms; replicated by independent labs\",\n      \"pmids\": [\"12857866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Smurf1 directly interacts with the osteoblast-specific transcription factor Runx2/Cbfa1 and mediates its ubiquitin- and proteasome-dependent degradation, controlling osteoblast differentiation.\",\n      \"method\": \"Co-IP, ubiquitination assay, proteasome inhibitor experiments, overexpression in osteoblast precursor cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding and ubiquitination demonstrated biochemically; replicated by multiple independent labs\",\n      \"pmids\": [\"12738770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Increased Smurf1 expression promotes myogenic differentiation of C2C12 cells and blocks BMP-induced osteogenic conversion by selectively reducing endogenous Smad5 levels while leaving TGF-β-pathway Smads (Smad2, 3, 7) unaffected; siRNA-mediated depletion of endogenous Smurf1 is required for normal myogenic differentiation.\",\n      \"method\": \"Overexpression, siRNA knockdown, Western blot, Smad5 rescue experiment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain- and loss-of-function combined with rescue experiment; selectivity for Smad5 mechanistically defined\",\n      \"pmids\": [\"12871975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Transgenic overexpression of Smurf1 in osteoblasts (under type I collagen promoter) significantly reduces bone formation in vivo, demonstrating a direct in vivo role for Smurf1 in suppressing osteoblast activity through BMP/Smad signaling components.\",\n      \"method\": \"Transgenic mouse generation, bone histomorphometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo transgenic model, single lab, no rescue experiment in this paper\",\n      \"pmids\": [\"14701828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Smurf1-deficient mice develop age-dependent bone mass increase due to enhanced osteoblast activity; mechanistically, Smurf1 physically interacts with MEKK2 and promotes its ubiquitination and proteasomal degradation, thereby suppressing downstream JNK signaling in osteoblasts independently of canonical Smad-mediated BMP/TGF-β signaling.\",\n      \"method\": \"Smurf1-knockout mice, Co-IP, in vitro ubiquitination assay, JNK pathway analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — genetic KO with phenotype, direct biochemical interaction and ubiquitination, pathway epistasis; published in Cell\",\n      \"pmids\": [\"15820682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Smurf1 ubiquitinates RhoA and physically interacts with it in neuroblastoma cells; overexpression of Smurf1 selectively reduces RhoA protein levels during cAMP-induced (but not retinoic acid-induced) neurite outgrowth, promoting neurite extension.\",\n      \"method\": \"Co-IP, ubiquitination assay, proteasome inhibitor, Neuro2a neurite outgrowth assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical interaction and functional assay in single lab; extends established RhoA-Smurf1 mechanism to neurons\",\n      \"pmids\": [\"15710384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"TNF-α up-regulates Smurf1 and Smurf2 expression in osteoblasts and promotes proteasomal degradation of Runx2, an effect blocked by siRNA against Smurf1, establishing that TNF-mediated Runx2 degradation requires Smurf1.\",\n      \"method\": \"siRNA knockdown, Western blot, proteasome inhibitor, reporter assay, in vivo TNF transgenic mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro siRNA epistasis and in vivo TNF transgenic data converge; replicated in the 2008 follow-up study\",\n      \"pmids\": [\"16373342\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Using Smurf1-deficient cells and siRNA knockdown, Smurf1 is identified as a rate-limiting, specific factor for ubiquitin-mediated proteasomal degradation of activated (CNF1-constitutively active) RhoA; ectopic Smurf1 restores RhoA ubiquitylation in Smurf1-deficient Vero cells.\",\n      \"method\": \"Smurf1-KO cells, siRNA, CNF1 toxin treatment, ubiquitination assay, rescue by ectopic Smurf1\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO plus siRNA plus rescue experiment; direct mechanistic demonstration of Smurf1 as the specific E3 for active RhoA\",\n      \"pmids\": [\"16540523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Smurf1-mediated RhoA degradation at the cell periphery reduces ROCK activity and myosin light chain 2 (MLC2) phosphorylation locally, enabling lamellipodia formation and 2D tumor cell motility; in 3D invasion, Smurf1 inhibition induces amoeboid-like transition and more invasive behavior.\",\n      \"method\": \"Smurf1 siRNA, ROCK activity assay, MLC2 phosphorylation, 2D and 3D invasion assays, in vivo tumor migration\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple assays (biochemical, 2D, 3D, in vivo) linking Smurf1-RhoA to ROCK/MLC2 in single study\",\n      \"pmids\": [\"17190792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"FKBP12 acts as an adaptor for the Smad7-Smurf1 complex on the activin type I receptor (ALK4); FK506, which dissociates FKBP12 from the receptor, decreases Smad7-Smurf1 interaction and inhibits TβR-I ubiquitination by Smurf1.\",\n      \"method\": \"Co-IP, ubiquitination assay, FK506 pharmacological interference\",\n      \"journal\": \"Journal of molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical interaction and pharmacological intervention, single lab\",\n      \"pmids\": [\"16720724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"LMP-1 interacts with the WW2 domain of Smurf1 via a PPxY-like motif and competes with Smad1/5 for Smurf1 binding, blocking ubiquitination of Smads and increasing BMP responsiveness.\",\n      \"method\": \"Co-IP, ubiquitination assay, competitive binding/peptide competition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct competition and ubiquitination assays, single lab\",\n      \"pmids\": [\"16611643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Smurf1 regulates neural patterning in Xenopus embryos by ubiquitin-mediated degradation of Smad1; morpholino-mediated Smurf1 knockdown elevates phospho-Smad1 levels in dorsal ectoderm and disrupts neural folding, placing Smurf1 as an antagonist of BMP/Smad1 signaling required for neural development.\",\n      \"method\": \"Antisense morpholino knockdown, dominant-negative protein, phospho-Smad1 Western blot, Xenopus embryology\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in Xenopus with biochemical readout, single lab\",\n      \"pmids\": [\"16973150\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Smurf2 interacts with Smurf1 and induces its ubiquitination and proteasomal degradation (but not vice versa), providing a post-translational mechanism for cross-regulation between these two related E3 ligases.\",\n      \"method\": \"Co-IP, ubiquitination assay, Western blot after Smurf2 knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical evidence in single lab with reciprocal experiments showing asymmetry\",\n      \"pmids\": [\"18927080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CKIP-1 specifically interacts with the linker region between the WW domains of Smurf1 (not Smurf2) and augments Smurf1's E3 ligase activity and substrate affinity; CKIP-1-deficient mice show age-dependent bone mass increase due to reduced Smurf1 activity.\",\n      \"method\": \"Co-IP, in vitro ubiquitination assay, domain mapping, CKIP-1 knockout mouse\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro ubiquitination assay with domain mapping, KO mouse phenotype, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"18641638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Smurf1 interacts with hPEM-2 (a GEF for Cdc42) via a Ca2+-independent C2 domain interaction (mapped to residues 318–343 of the PH domain of hPEM-2) and induces its proteasomal degradation.\",\n      \"method\": \"GST pull-down, pulse-chase labeling, proteasome inhibitor, domain mapping\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical interaction and degradation assays, domain-level mapping, single lab\",\n      \"pmids\": [\"18208356\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Talin head (generated by calpain cleavage of talin) binds Smurf1 more tightly than full-length talin and is ubiquitylated by Smurf1 leading to its degradation; Cdk5 phosphorylates talin head at Ser425, which inhibits Smurf1 binding and prevents its degradation, thereby stabilizing focal adhesions and supporting cell migration.\",\n      \"method\": \"Co-IP, in vitro ubiquitination assay, kinase assay, phospho-mimetic/phospho-resistant mutants, focal adhesion assays, cell migration assay\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — reconstitution-level biochemistry (kinase assay + ubiquitination + phospho-mutants) combined with functional migration readout; published in Nature Cell Biology\",\n      \"pmids\": [\"19363486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Smurf1 interacts with TRAF4 via TRAF4's PY motifs and the second WW domain of Smurf1, promoting ubiquitination and degradation of TRAF4; Smurf1 can ubiquitinate all six TRAF family members and thereby attenuates NF-κB signaling.\",\n      \"method\": \"Yeast two-hybrid, Co-IP, ubiquitination assay, NF-κB reporter\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus Co-IP plus functional reporter, single lab\",\n      \"pmids\": [\"19937093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Smurf1 interacts with JunB via its PY motif and targets JunB for ubiquitination and proteasomal degradation; Smurf1-deficient MSCs have elevated JunB, increased cyclin D1, and enhanced osteoblast differentiation, placing Smurf1-JunB in a pathway controlling MSC proliferation.\",\n      \"method\": \"Co-IP, ubiquitination assay, Smurf1-KO cells, JunB knockdown/rescue\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical methods plus KO cells plus rescue\",\n      \"pmids\": [\"20200942\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The C2 domain of Smurf1 is necessary and sufficient to bind RhoA and is required for RhoA ubiquitination; the C2 domain is dispensable for Smad1 ubiquitination, revealing a substrate-selective role of the C2 domain. Two key lysines (K28 and K85) in the C2 domain are critical for plasma membrane localization and robust RhoA-directed ligase activity.\",\n      \"method\": \"Domain deletion/point mutants, GST pull-down, ubiquitination assay, crystal structure of C2 domain, cell migration assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure + mutagenesis + in vitro ubiquitination assay + functional cell assay in single study\",\n      \"pmids\": [\"21402695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The C2 domain of Smurf1 is necessary and sufficient to bind RhoA (and also Axin), while the C2-HECT autoinhibitory mechanism observed in Smurf2 does not operate in Smurf1; instead, Smurf1's C2 domain functions in substrate selection rather than autoinhibition.\",\n      \"method\": \"FRET, Co-IP, domain deletion mutants, ubiquitination assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical domain mapping, single lab, complements crystal structure paper\",\n      \"pmids\": [\"21708152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Cdh1 (APC/C adaptor) promotes Smurf1 E3 ligase activity independently of APC/C E3 activity by disrupting an autoinhibitory Smurf1 homodimer; Cdh1 depletion reduces Smurf1 activity, leading to MEKK2 accumulation and JNK activation, which drives osteoblast differentiation.\",\n      \"method\": \"Co-IP, in vitro ubiquitination assay, siRNA, homodimer disruption assay, osteoblast differentiation readout\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical demonstration of homodimer disruption plus E3 activity assay plus signaling and differentiation phenotype\",\n      \"pmids\": [\"22152476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The SCF(FBXL15) ubiquitin ligase complex targets Smurf1 for ubiquitination and proteasomal degradation; FBXL15 specifically recognizes the HECT domain N-lobe of Smurf1 and ubiquitinates it at K355/K357, thereby positively regulating BMP signaling.\",\n      \"method\": \"Co-IP, ubiquitination assay, domain mapping, siRNA knockdown in zebrafish, siRNA injection in rat bone\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — site-specific ubiquitination mapping plus multi-organism functional validation\",\n      \"pmids\": [\"21572392\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Smurf1 interacts with WFS1 (Wolfram syndrome protein) at the ER via the C-terminal luminal region of WFS1 (residues 667–700) and promotes its ubiquitination and proteasomal degradation; ER stress induces Smurf1 degradation and WFS1 up-regulation, suggesting feedback regulation.\",\n      \"method\": \"Co-IP, ubiquitination assay, domain mapping, siRNA, ER stress inducers\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical interaction and ubiquitination with domain mapping, single lab\",\n      \"pmids\": [\"21454619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Smurf1 interacts with and ubiquitinates KLF2 for proteasomal degradation specifically in lung cancer H1299 cells, requiring Smurf1's catalytic activity; this represses KLF2 transcriptional activity and alters expression of downstream targets (CD62L, Wee1).\",\n      \"method\": \"Co-IP, ubiquitination assay, catalytic mutant, reporter assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical interaction and ubiquitination with functional readout, single lab\",\n      \"pmids\": [\"21382345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PKA-dependent phosphorylation of Smurf1 at Thr306 switches its substrate preference: Thr306-phosphorylated Smurf1 preferentially degrades RhoA over Par6; preventing this phosphorylation reduces axon formation in hippocampal neurons and impairs cortical neuron polarization in vivo.\",\n      \"method\": \"PKA phosphorylation assay, phospho-mimetic/resistant mutants, in vitro ubiquitination, cultured neuron axon formation assay, in utero electroporation\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — kinase assay + ubiquitination + phospho-mutants + in vivo cortical polarization; multiple orthogonal methods\",\n      \"pmids\": [\"21262463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Ndfip1 enhances Smurf1 self-ubiquitination and its interaction with MAVS, promoting MAVS ubiquitination and degradation; Ndfip1 knockdown elevates MAVS levels and enhances RIG-I-dependent antiviral signaling.\",\n      \"method\": \"Co-IP, ubiquitination assay, siRNA knockdown, IFN-β reporter, IRF-3 phosphorylation assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical interaction and functional signaling assays, single lab\",\n      \"pmids\": [\"23087404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Smurf1 interacts with STAT1 through its WW domains and the PY motif of STAT1, catalyzing K48-linked polyubiquitination and proteasomal degradation of STAT1 independently of STAT1 phosphorylation; Smurf1 overexpression attenuates IFN-γ signaling and antiviral response, while knockdown enhances them.\",\n      \"method\": \"Co-IP, domain mapping, ubiquitination assay (K48-linkage), siRNA, IFN-γ reporter, antiviral assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — domain-level interaction mapping, linkage-specific ubiquitination assay, gain/loss-of-function with functional signaling readouts\",\n      \"pmids\": [\"22474288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Deubiquitinase USP9X (FAM) interacts with Smurf1 via the second WW domain of Smurf1 and the C-terminus of USP9X, antagonizing Smurf1 autoubiquitination and protecting Smurf1 from self-degradation; USP9X depletion leads to Smurf1 down-regulation and impaired cell migration.\",\n      \"method\": \"Quantitative MS, Co-IP, domain mapping, ubiquitination assay, siRNA, migration assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mass spectrometry interactomics validated by Co-IP and domain mapping plus functional migration readout\",\n      \"pmids\": [\"23184937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Smurf1 ubiquitinates Axin via atypical K29-linked polyubiquitin chains (at K789 and K821) without inducing degradation; this modification disrupts Axin's interaction with LRP5/6 co-receptors and attenuates Wnt-stimulated LRP6 phosphorylation, thereby repressing Wnt/β-catenin signaling.\",\n      \"method\": \"Co-IP, in vitro ubiquitination assay, K29-linkage-specific analysis, site-directed mutagenesis, Wnt reporter, Smurf1-KO MEFs\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — linkage-specific ubiquitination with mutagenesis, functional reporter, KO fibroblasts; multiple orthogonal methods\",\n      \"pmids\": [\"23959799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Smurf1 induces non-degradative ubiquitination of TRAF4 at K190, which is required for proper localization of TRAF4 to tight junctions in confluent epithelial cells; this ubiquitination event is essential for TRAF4-mediated Rac1 activation and breast epithelial/cancer cell migration.\",\n      \"method\": \"Co-IP, ubiquitination assay with K190R mutant, localization by microscopy, Rac1 activation assay, migration assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — site-specific ubiquitination with functional mutant rescue, localization assay, Rac1 GEF activity, and migration phenotype\",\n      \"pmids\": [\"23760265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Smurf1 directly interacts with and ubiquitinates TRIB2 (at a N-terminal domain, residues 1–5), a process requiring prior p70S6K-mediated phosphorylation of TRIB2 at Ser83; reduced p70S6K and Smurf1 in liver cancer leads to increased TRIB2 stability.\",\n      \"method\": \"Co-IP, ubiquitination assay, domain mapping, phospho-mutant analysis, half-life assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction and ubiquitination with domain and phospho-mutant mapping, single lab\",\n      \"pmids\": [\"24089522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PKA-mediated phosphorylation of Smurf1 at Thr306 prevents JNK-triggered Nur77 degradation by enabling unconventional (non-degradative) ubiquitination of Nur77 by Smurf1, resulting in Nur77 accumulation and mitochondrial translocation to induce apoptosis in cisplatin-treated cells.\",\n      \"method\": \"PKA phosphorylation assay, ubiquitination assay, Nur77 stability assay, apoptosis readout, phospho-mimetic mutants\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical kinase and ubiquitination assays with functional apoptosis readout, single lab\",\n      \"pmids\": [\"23584473\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Smurf1 is activated by neddylation: Smurf1 physically interacts with Nedd8 and Ubc12, forms a Nedd8-thioester intermediate, and auto-neddylates itself on multiple lysines via an active site at C426 in the HECT N-lobe; neddylation of Smurf1 enhances ubiquitin E2 recruitment and ubiquitin ligase activity. This regulatory mechanism is conserved in yeast Rsp5.\",\n      \"method\": \"In vitro neddylation assay, Nedd8-thioester intermediate detection, active-site mutagenesis (C426), yeast Rsp5 conservation test, ubiquitin E2 recruitment assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro neddylation, active-site mutagenesis, mechanistic thioester intermediate trapping, evolutionary conservation\",\n      \"pmids\": [\"24821572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"DNA damage (UV or MMS) activates ATR/Chk1, which phosphorylates Smurf1, enhancing Smurf1 self-degradation; this leads to RhoB accumulation and apoptosis. In the basal state, Smurf1 targets RhoB for degradation to control its abundance.\",\n      \"method\": \"Kinase assay, Smurf1 phospho-mutants, ubiquitination assay, apoptosis assay, Smurf1 overexpression/KD\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ATR/Chk1/Smurf1 pathway defined by biochemical kinase assay and phospho-mutants with functional cell fate readout\",\n      \"pmids\": [\"25249323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The C2 domain of Smurf1 mediates its interaction with Axin in a non-canonical manner (independent of WW-PY interaction); plasma membrane localization via the C2 domain is required for Axin ubiquitination. Smurf1-Axin interaction and K29-linked ubiquitination are attenuated in G2/M phase, correlating with increased Wnt responsiveness at that cell cycle stage.\",\n      \"method\": \"Co-IP, domain mapping, ubiquitination assay, cell cycle synchronization, Wnt reporter\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain mapping and cell cycle correlation, single lab building on prior Axin finding\",\n      \"pmids\": [\"24700460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Smurf1 is required for selective autophagy of Mycobacterium tuberculosis (Mtb) in macrophages; Smurf1-/- macrophages fail to recruit polyubiquitin, NBR1, LC3, and LAMP1 to Mtb-associated structures. This function requires both the ubiquitin-ligase and C2 phospholipid-binding domains and involves K48-linked ubiquitination. Smurf1-/- mice show increased bacterial load and accelerated mortality.\",\n      \"method\": \"Smurf1-/- macrophages, domain mutant analysis, K48/K63-linkage ubiquitination assay, confocal microscopy for autophagy markers, in vivo mouse infection\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with in vivo infection, domain dissection, linkage-specific ubiquitination, multiple autophagy markers\",\n      \"pmids\": [\"28017659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"AMPK-mediated phosphorylation of Smurf1 at Ser148 controls osteoblast differentiation: a S148A knock-in mutation (preventing AMPK phosphorylation) causes premature osteoblast differentiation phenotype equivalent to Smurf1-/-, high bone mass, and hyperinsulinemia/hypoglycemia through increased Runx2 accumulation and elevated insulin receptor levels (Smurf1 also targets the insulin receptor for degradation).\",\n      \"method\": \"Smurf1 S148 knock-in mouse, Runx2 protein levels, insulin receptor degradation assay, phosphorylation by AMPK\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knock-in mouse with precise phospho-site and multiple downstream readouts\",\n      \"pmids\": [\"27052174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Smurf1 deletion protects mice from pulmonary arterial hypertension; SMURF1 is identified as a key miR-140-5p target in PASMCs; SMURF1 knockdown alters BMP signaling in smooth muscle cells.\",\n      \"method\": \"Smurf1-/- mouse PAH model, miR-140-5p mimic delivery, SMURF1 siRNA, BMP signaling reporter\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO mouse and RNAi in disease model; mechanism via BMP signaling regulation\",\n      \"pmids\": [\"27214554\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Smurf1 interacts with Kindlin-2 and promotes its ubiquitination and degradation, thereby inhibiting αIIbβ3 and β1 integrin activation; Smurf1-KO MEFs show enhanced β1 integrin activation correlated with increased Kindlin-2 protein levels. Smurf1 selectively degrades Kindlin-2 but not Talin.\",\n      \"method\": \"Co-IP, ubiquitination assay, integrin activation assay, Smurf1-KO MEFs, colon cancer tissue correlation\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO cells plus biochemical ubiquitination plus functional integrin assay plus substrate selectivity demonstration\",\n      \"pmids\": [\"28408404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Smurf1 directly interacts with PIPKIγ via its C2 domain and ubiquitinates PIPKIγ at K255, targeting it for degradation; PKA-mediated phosphorylation of Smurf1 at Thr306 (or Smurf1-T306D phospho-mimetic) prevents PIPKIγ degradation, linking PKA-Smurf1 signaling to lung cancer cell growth.\",\n      \"method\": \"Co-IP, ubiquitination assay, domain mapping, phospho-mimetic mutants, in vitro kinase assay, tumor growth assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical interaction, ubiquitination site mapping, phospho-mutant analysis, single lab\",\n      \"pmids\": [\"28581524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SMURF1 interacts with ERα via its HECT domain and inhibits K48-specific polyubiquitination of ERα, stabilizing ERα protein and promoting ERα-dependent transcription and breast cancer cell proliferation.\",\n      \"method\": \"Co-IP with domain mapping, ubiquitin immunoprecipitation (K48-specific), protein stability assay, ERα reporter, siRNA, xenograft\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction mapped to HECT domain, K48-ubiquitination assay, functional reporter and cell/xenograft phenotype, single lab\",\n      \"pmids\": [\"29433542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Smurf1 mediates non-proteolytic K63-linked ubiquitination of PPARγ, suppressing its transcriptional activity; Smurf1-deficient mice develop spontaneous hepatic steatosis with up-regulated PPARγ target genes, and PPARγ antagonist treatment fully reverses lipid accumulation.\",\n      \"method\": \"Smurf1-KO mouse, K63-linkage-specific ubiquitination assay, PPARγ reporter, PPARγ antagonist rescue, high-fat diet experiment\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — genetic KO mouse, linkage-specific ubiquitination, pharmacological rescue; multiple orthogonal methods\",\n      \"pmids\": [\"30566427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SMURF1 is expressed at the primary cilium and at the outflow tract cushion mesenchyme during heart development; Smurf1-/- embryos show delayed outflow tract septation and reduced aortic smooth muscle layer thickness; Smurf1 promotes smooth muscle and cardiac fibroblast differentiation while negatively regulating cardiomyogenesis.\",\n      \"method\": \"Smurf1-/- mouse embryos, immunofluorescence localization to primary cilium, histomorphometry, differentiation marker analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse phenotype plus localization to cilium; differentiation assays, single lab\",\n      \"pmids\": [\"29934521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CKIP-1 and Smurf1 are co-expressed at the chick neural plate border; CKIP-1 knockdown causes neural crest loss by suppressing BMP/pSmad1/5/8 signaling; Smurf1 overexpression mimics CKIP-1 loss (both reduce pSmad1/5/8); epistasis shows CKIP-1 rescues Smurf1-mediated neural crest loss by suppressing Smurf1-mediated Smad degradation.\",\n      \"method\": \"Morpholino knockdown, Smurf1 overexpression, BMP reporter, pSmad1/5/8 Western blot, epistasis (CKIP-1 rescue of Smurf1 OE)\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple pathway readouts, in vivo chick model\",\n      \"pmids\": [\"29949573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SMURF1 ubiquitinates UVRAG at K517 and K559 via K29/K33-linked polyubiquitin chains, reducing UVRAG-RUBCN association and promoting autophagosome maturation; CSNK1A1-mediated phosphorylation of UVRAG at Ser522 blocks SMURF1 binding to UVRAG; deubiquitinase ZRANB1 removes SMURF1-catalyzed chains from UVRAG, restoring RUBCN binding.\",\n      \"method\": \"Co-IP, in vitro ubiquitination assay, site-directed mutagenesis, autophagosome maturation assay, kinase assay, deubiquitinase assay\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — site-specific ubiquitination, linkage determination, phospho-mutant regulation, orthogonal DUB and kinase assays, in vitro and in vivo evidence\",\n      \"pmids\": [\"30686098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SMURF1 interacts with and ubiquitinates ARHGAP26, a negative regulator of RhoA (RhoA-GAP), promoting its degradation and thereby sustaining RhoA-GTP levels, which activates β-catenin signaling and promotes ovarian cancer cell invasion and migration.\",\n      \"method\": \"Co-IP, ubiquitination assay, ARHGAP26 overexpression/knockdown, RhoA-GTP pull-down, in vivo lung metastasis assay\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction and ubiquitination assay with functional rescue, single lab\",\n      \"pmids\": [\"31004081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Smurf1 ubiquitylates and degrades PTEN, leading to PI3K/Akt/mTOR pathway activation; Smurf1-deficient glioblastoma cells have restored PTEN activity, reduced PI3K/Akt signaling, and are sensitized to rapamycin; combined Smurf1 knockdown plus rapamycin reduces tumor progression in an orthotopic GBM model.\",\n      \"method\": \"Co-IP, ubiquitination assay, PTEN activity assay, Smurf1 siRNA, in vivo orthotopic GBM model, rapamycin combination\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct ubiquitination and functional tumor model, single lab\",\n      \"pmids\": [\"32737433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Smurf1 acts as a Nedd8 ligase (in addition to ubiquitin ligase) to catalyze neddylation of RRP9 (U3 snoRNP component) primarily at K221; RRP9 neddylation promotes pre-rRNA processing and ribosome biogenesis; unneddylated RRP9-K221R lacks tumor-promoting activity. NEDP1 removes Nedd8 from RRP9.\",\n      \"method\": \"In vivo and in vitro neddylation assay, site-directed mutagenesis (K221R), pre-rRNA processing assay, co-IP, functional tumor proliferation/migration assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro neddylation, site mapping by mutagenesis, deneddylase identification, functional ribosome biogenesis assay\",\n      \"pmids\": [\"34662580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SMURF1 ubiquitylates and degrades SHP-1 (a protein tyrosine phosphatase), activating STAT3 signaling; SMURF1 and SHP-1 protein levels are inversely correlated in endometriosis tissue, and SMURF1-mediated SHP-1 degradation promotes endometrial stromal cell proliferation and invasion.\",\n      \"method\": \"Co-IP, ubiquitination assay, Co-IP in patient tissues, siRNA/overexpression, STAT3 activation assay, invasion assay\",\n      \"journal\": \"Annals of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical interaction/ubiquitination with functional cellular readout, single lab\",\n      \"pmids\": [\"33842583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ERK phosphorylates Smurf1 at Thr223 upon TGFβ stimulation; this phosphorylation is a prerequisite for Smurf1-mediated RhoA polyubiquitination and degradation, cytoskeletal rearrangement, and EMT; blocking Thr223 phosphorylation inhibits TGFβ-induced EMT and dramatically reduces lung metastasis of murine breast cancer in vivo.\",\n      \"method\": \"Kinase assay, phospho-mutants, Co-IP, ubiquitination assay, EMT markers, in vivo lung metastasis\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — kinase phosphorylation site identified and functionally validated with phospho-mutants in vitro and in vivo metastasis model\",\n      \"pmids\": [\"35654587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Smurf1 interacts with the TGR5 intracellular loop 2 (ICL2) region via its HECT domain and mediates K11/K48-linked polyubiquitination of TGR5 at K306, leading to proteasomal degradation of TGR5 under high glucose stimulation; genetic Smurf1 deficiency restores TGR5 and attenuates renal injury in diabetic mice.\",\n      \"method\": \"Co-IP, domain mapping, site-directed mutagenesis (K306R), K11/K48-linkage-specific ubiquitination assay, Smurf1-KO diabetic mouse model\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — site-specific ubiquitination with domain mapping and mutagenesis, linkage determination, and KO mouse phenotype\",\n      \"pmids\": [\"37481723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Smurf1 triggers PDK1 neddylation upon growth factor stimulation; poly-Nedd8 chains on PDK1 recruit methyltransferase SETDB1 to form a cytoplasmic complex (cCOMPASS: PDK1-Smurf1-SETDB1) that directs Akt membrane attachment and T308 phosphorylation; Smurf1 deficiency reduces CRC tumorigenesis; a Smurf1-specific degrader (SART-1) blocks PDK1-Akt signaling and suppresses KRAS-mutated CRC tumors.\",\n      \"method\": \"In vitro neddylation assay, Co-IP, Smurf1 genetic KO in CRC mouse model, Akt membrane recruitment assay, Smurf1 PROTAC degrader, PDK1 inhibitor combination\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — reconstituted neddylation, complex identification, genetic KO mouse model, pharmacological degrader with mechanism validation\",\n      \"pmids\": [\"39039255\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SMURF1 is a HECT-domain E3 ubiquitin ligase (and Nedd8 ligase) that uses its C2 domain for membrane targeting and substrate selection, its WW domains for PY-motif-containing substrates, and its HECT domain for catalysis; it is activated by neddylation (auto-catalyzed via C426) and by co-factors CKIP-1 and Cdh1, regulated by PKA/Chk1/ERK/AMPK/IRAK2-mediated phosphorylation that can switch substrate preference (e.g., RhoA vs. Par6) or trigger self-degradation, and it ubiquitinates a broad set of substrates—including Smad1/5, Runx2, RhoA, RhoB, MEKK2, TGF-β/BMP receptors (via Smad7), MAVS, STAT1, talin head, Kindlin-2, TRAF proteins, JunB, Axin (K29-linked, non-degradative), PPARγ (K63-linked, non-degradative), UVRAG, PTEN, TGR5, and PDK1 (neddylation)—thereby controlling BMP/TGF-β signaling, osteoblast differentiation, Wnt/β-catenin signaling, cell polarity and migration, autophagy, antiviral immunity, metabolic homeostasis, and PI3K-Akt-driven tumorigenesis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SMURF1 is a HECT-domain E3 ubiquitin ligase that governs cellular responses to the BMP/TGF-\\u03b2 family, cell polarity and migration, and several metabolic and immune programs by selectively ubiquitinating signaling proteins [#0, #6]. Its founding activity is the negative regulation of TGF-\\u03b2/BMP signaling: SMURF1 binds the inhibitory Smad7, ubiquitinates it, and uses it as an adaptor to recruit and degrade the type I receptor, and it cooperates with inhibitory Smads to degrade BMP receptors and Smad1/5, thereby antagonizing osteoblastic differentiation and patterning [#0, #2, #4]. A C2 domain provides membrane targeting and substrate selection \\u2014 it is required to localize the SMURF1\\u2013Smad7 complex to the plasma membrane and is necessary and sufficient to bind substrates such as RhoA and Axin, while the WW domains capture PY-motif substrates and the HECT domain catalyzes transfer [#1, #20, #21]. SMURF1 controls cell motility by degrading active RhoA locally to limit ROCK/MLC2 signaling and enable lamellipodial protrusion [#9, #10], and it shapes adhesion through degradation of talin head and Kindlin-2 [#17, #40]. Beyond canonical degradative ubiquitination, SMURF1 installs non-proteolytic chains: K29-linked ubiquitination of Axin disrupts LRP6 coupling to repress Wnt/\\u03b2-catenin signaling, K63-linked ubiquitination of PPAR\\u03b3 suppresses its transcription to restrain hepatic lipid accumulation, and K29/K33-linked ubiquitination of UVRAG promotes autophagosome maturation [#30, #43, #46]. SMURF1 is also required for selective autophagy of intracellular Mycobacterium tuberculosis and attenuates antiviral and cytokine signaling by degrading MAVS and STAT1 [#37, #27, #28]. The enzyme is auto-activated by neddylation through an active-site cysteine (C426), and additionally acts as a Nedd8 ligase toward substrates: it neddylates RRP9 to promote ribosome biogenesis and neddylates PDK1 to assemble a cytoplasmic PDK1\\u2013SMURF1\\u2013SETDB1 complex driving Akt activation and KRAS-mutant tumorigenesis [#34, #49, #53]. SMURF1 activity is tuned by co-factors (CKIP-1, Cdh1) and by kinase inputs \\u2014 PKA phosphorylation at Thr306, ERK at Thr223, AMPK at Ser148, and ATR/Chk1 \\u2014 that switch substrate preference or trigger self-degradation [#15, #22, #26, #51, #38, #35].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established the founding function of SMURF1 as a negative regulator of TGF-\\u03b2 signaling by showing it ubiquitinates Smad7 and uses it to target the type I receptor.\",\n      \"evidence\": \"Co-IP and ubiquitination assays in mammalian cells\",\n      \"pmids\": [\"11278251\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the ubiquitin chain linkage\", \"Did not address regulation of SMURF1 activity itself\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identified the C2 domain as the membrane-targeting module required for receptor recruitment, answering how the ligase reaches its membrane substrates.\",\n      \"evidence\": \"C2-deletion mutants with localization, Co-IP, and ubiquitination assays\",\n      \"pmids\": [\"12151385\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of C2 membrane/substrate binding not resolved here\", \"Did not test C2 role for non-receptor substrates\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Extended the inhibitory repertoire to BMP receptors and the osteoblast transcription factor Runx2, placing SMURF1 at the center of bone/skeletal differentiation control.\",\n      \"evidence\": \"Xenopus axis and reporter assays, Co-IP and ubiquitination in osteoblast precursors, Smad5-selective degradation with rescue\",\n      \"pmids\": [\"12857866\", \"12738770\", \"12871975\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Selectivity determinants distinguishing Smad5 from Smad2/3 not mapped\", \"In vivo bone consequence not yet shown in these reports\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic loss-of-function defined SMURF1 as a physiological suppressor of osteoblast activity and revealed a Smad-independent axis through MEKK2/JNK.\",\n      \"evidence\": \"Smurf1-knockout mice with bone phenotype, Co-IP, in vitro ubiquitination, and JNK epistasis; RhoA degradation shown in neurons\",\n      \"pmids\": [\"15820682\", \"15710384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SMURF1 partitions between Smad and MEKK2 substrates in vivo unclear\", \"Upstream signals selecting MEKK2 not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined SMURF1 as the rate-limiting, specific E3 for activated RhoA and linked this to localized cytoskeletal control of migration and invasion.\",\n      \"evidence\": \"Smurf1-KO cells with rescue, CNF1 activation, ROCK/MLC2 readouts, 2D/3D invasion and in vivo migration assays\",\n      \"pmids\": [\"16540523\", \"17190792\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatial mechanism restricting RhoA degradation to the cell periphery not fully resolved\", \"Determinants of active- versus inactive-RhoA recognition unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified co-factor and cross-regulatory control of SMURF1 activity, showing CKIP-1 augments its ligase activity and Smurf2 degrades it.\",\n      \"evidence\": \"Co-IP, domain mapping, in vitro ubiquitination, and CKIP-1 knockout mouse bone phenotype\",\n      \"pmids\": [\"18641638\", \"18927080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which CKIP-1 increases catalytic output not structurally defined\", \"Physiological trigger for Smurf2-mediated SMURF1 turnover unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed SMURF1 controls focal-adhesion turnover by degrading the calpain-generated talin head, and that Cdk5 phosphorylation of talin protects it, integrating proteolysis into adhesion dynamics.\",\n      \"evidence\": \"Co-IP, in vitro ubiquitination, kinase assay, phospho-mutants, focal adhesion and migration assays\",\n      \"pmids\": [\"19363486\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether full-length talin is ever a substrate in vivo unclear\", \"Coordination with RhoA-directed activity during migration not addressed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Provided structural and mechanistic dissection: the C2 domain mediates substrate selection (RhoA, Axin) rather than Smurf2-type autoinhibition, and Cdh1 activates SMURF1 by disrupting an autoinhibitory homodimer.\",\n      \"evidence\": \"C2 crystal structure with mutagenesis, FRET, ubiquitination assays, and Cdh1 homodimer-disruption and osteoblast differentiation readouts; SCF(FBXL15) shown to degrade SMURF1\",\n      \"pmids\": [\"21402695\", \"21708152\", \"22152476\", \"21572392\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length SMURF1 structure and chain-type determinants not resolved\", \"How Cdh1 and CKIP-1 inputs are integrated unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Revealed PKA phosphorylation at Thr306 as a substrate-preference switch directing SMURF1 toward RhoA over Par6 to control neuronal polarization.\",\n      \"evidence\": \"PKA kinase assay, phospho-mutants, in vitro ubiquitination, neuronal axon-formation assay, in utero electroporation\",\n      \"pmids\": [\"21262463\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of phospho-driven substrate switching not defined\", \"Other kinases acting at the same site not yet identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Connected SMURF1 to antiviral and cytokine signaling by degrading MAVS (with Ndfip1) and K48-ubiquitinating STAT1, and identified USP9X as a stabilizing deubiquitinase.\",\n      \"evidence\": \"Co-IP, linkage-specific ubiquitination, siRNA, IFN reporters, and mass-spectrometry interactomics\",\n      \"pmids\": [\"23087404\", \"22474288\", \"23184937\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo immune phenotypes of these substrate relationships not established here\", \"Balance between USP9X protection and Smurf2/FBXL15 turnover unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated that SMURF1 builds non-degradative ubiquitin chains \\u2014 K29-linked on Axin to repress Wnt and K190 on TRAF4 for localization \\u2014 expanding its output beyond proteasomal degradation.\",\n      \"evidence\": \"Linkage-specific and site-specific ubiquitination assays, mutagenesis, Wnt reporters, Smurf1-KO MEFs, Rac1 activation and migration assays\",\n      \"pmids\": [\"23959799\", \"23760265\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SMURF1 selects chain linkage per substrate is unknown\", \"Readers decoding the K29 Axin chain not identified\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified neddylation as a core regulatory mechanism: SMURF1 auto-neddylates via C426 to boost E2 recruitment and ligase activity, and DNA-damage Chk1 signaling drives SMURF1 self-degradation to permit RhoB-dependent apoptosis.\",\n      \"evidence\": \"Reconstituted in vitro neddylation, thioester trapping, active-site mutagenesis, yeast Rsp5 conservation; kinase assays and phospho-mutants for the Chk1 axis\",\n      \"pmids\": [\"24821572\", \"25249323\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous triggers of SMURF1 auto-neddylation in cells not defined\", \"Phospho-sites mediating Chk1-driven self-degradation not fully mapped\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established SMURF1 as a mediator of selective xenophagy and an AMPK-controlled metabolic node, requiring its C2 and ligase domains for anti-mycobacterial autophagy and Ser148 phosphorylation for osteoblast/insulin-receptor control.\",\n      \"evidence\": \"Smurf1-/- macrophages and infection in mice, domain and linkage analysis; Smurf1 S148A knock-in mouse with bone and glucose phenotypes\",\n      \"pmids\": [\"28017659\", \"27052174\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct ubiquitinated cargo on Mtb-associated structures not fully defined\", \"How AMPK phosphorylation alters catalytic behavior mechanistically unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined a metabolic role through non-degradative K63 ubiquitination of PPAR\\u03b3, with Smurf1 loss causing hepatic steatosis reversible by PPAR\\u03b3 antagonism.\",\n      \"evidence\": \"Smurf1-KO mouse, K63-linkage-specific ubiquitination, PPAR\\u03b3 reporter, pharmacological rescue, high-fat diet\",\n      \"pmids\": [\"30566427\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific contribution of SMURF1 to lipid metabolism not dissected\", \"Coordination with other PPAR\\u03b3 regulators unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed SMURF1 promotes autophagosome maturation by K29/K33-ubiquitinating UVRAG, with kinase and DUB inputs (CSNK1A1, ZRANB1) gating the modification.\",\n      \"evidence\": \"Co-IP, site-specific and linkage-determined ubiquitination, autophagosome maturation, kinase and deubiquitinase assays\",\n      \"pmids\": [\"30686098\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How UVRAG ubiquitination integrates with the xenophagy role unclear\", \"Structural recognition of UVRAG sites not resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Expanded SMURF1 to a bona fide Nedd8 ligase by showing it neddylates RRP9 to promote pre-rRNA processing and ribosome biogenesis.\",\n      \"evidence\": \"In vivo/in vitro neddylation, K221R mutagenesis, pre-rRNA processing assay, NEDP1 deneddylation, tumor proliferation assays\",\n      \"pmids\": [\"34662580\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants distinguishing ubiquitin versus Nedd8 transfer not defined\", \"Scope of the SMURF1 neddylome unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified ERK phosphorylation at Thr223 as a TGF\\u03b2-induced prerequisite for RhoA degradation, EMT, and metastasis, providing a druggable kinase\\u2013ligase link.\",\n      \"evidence\": \"Kinase assay, phospho-mutants, Co-IP, ubiquitination, EMT markers, in vivo lung metastasis\",\n      \"pmids\": [\"35654587\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Interplay between Thr223 (ERK) and Thr306 (PKA) phospho-control not resolved\", \"Whether other migration substrates respond to Thr223 status unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked SMURF1 neddylase activity to oncogenic Akt signaling: PDK1 neddylation assembles a cytoplasmic PDK1\\u2013SMURF1\\u2013SETDB1 complex driving Akt activation, and a SMURF1 degrader suppresses KRAS-mutant tumors.\",\n      \"evidence\": \"In vitro neddylation, complex identification, Smurf1-KO CRC mouse model, Akt membrane-recruitment assay, PROTAC degrader\",\n      \"pmids\": [\"39039255\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SETDB1 methyltransferase activity contributes mechanistically unclear\", \"Selectivity and broader effects of the degrader not fully characterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how SMURF1 selects between proteasomal versus non-degradative chain linkages and between ubiquitin versus Nedd8 transfer for a given substrate, and how its many kinase and co-factor inputs are integrated on a single full-length enzyme.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No full-length structure capturing substrate, co-factor, and chain-type selection\", \"No unified model reconciling competing phospho-inputs (PKA/ERK/AMPK/Chk1)\", \"Determinants of ubiquitin-versus-Nedd8 cofactor choice undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3, 6, 9, 28, 40]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 34, 49]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1, 20, 37]},\n      {\"term_id\": \"GO:0031386\", \"supporting_discovery_ids\": [34, 49, 53]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 10, 20, 36]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 53]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [44]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 6, 30]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [37, 46]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [27, 28]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [38, 43]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 5, 6, 13, 44]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 3, 34]}\n    ],\n    \"complexes\": [\"PDK1-SMURF1-SETDB1 (cCOMPASS)\"],\n    \"partners\": [\"SMAD7\", \"RHOA\", \"AXIN1\", \"CKIP-1\", \"MEKK2\", \"USP9X\", \"UVRAG\", \"TRAF4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}