{"gene":"TNFSF9","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2018,"finding":"Crystal structures of the human 4-1BB/4-1BBL complex, unbound 4-1BBL, and 4-1BB bound to utomilumab or urelumab were solved, revealing: (1) 4-1BBL forms a canonical bell-shaped trimer (not the previously reported three-bladed propeller), (2) 4-1BB binds predominantly to one protomer of the 4-1BBL trimer at the inter-protomer crevice via a distinct mechanism lacking the canonical DE-loop tyrosine interaction, (3) utomilumab binds 4-1BB CRDs 3–4 and blocks ligand, whereas urelumab binds CRD-1 away from the ligand-binding site, and (4) cell-based assays show utomilumab is a milder agonist than urelumab.","method":"X-ray crystallography (structures of complex, ligand alone, and antibody-bound receptor); cell-based functional assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple crystal structures with functional validation, replicated by two independent structural studies published simultaneously (PMIDs 30410017, 29720398, 29720399)","pmids":["30410017"],"is_preprint":false},{"year":2018,"finding":"Crystal structure of the human 4-1BB/4-1BBL complex at 2.4 Å resolution shows 4-1BBL adopts a canonical bell-shaped trimer (contradicting a previously published propeller structure). Mutational data support this structure as biologically relevant. 4-1BB forms a disulfide-linked dimer via a CRD4 cysteine, and this covalent receptor dimerization can cross-link ligand-receptor complexes into a 2D signaling network, amplifying 4-1BB signaling.","method":"X-ray crystallography; site-directed mutagenesis; structural comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — independent crystal structure with mutagenesis, corroborated by PMID 30410017 published simultaneously","pmids":["29720398","29720399"],"is_preprint":false},{"year":2018,"finding":"Crystal structure of mouse 4-1BBL reveals a disulfide-linked dimeric assembly (unlike trimeric human 4-1BBL), mediated by Cys-246 and Ser-256 unique to m4-1BBL. Upon m4-1BB binding, m4-1BBL undergoes structural changes within each protomer and inter-subunit rotation. Each receptor monomer binds a single ligand subunit via CRD1, CRD2, and CRD3, with the GH loop (not DE loop) providing energetically critical contacts defining receptor selectivity.","method":"X-ray crystallography; structure-guided mutagenesis of binding interface","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures of free and complexed m4-1BBL with mutagenesis validation","pmids":["30545939"],"is_preprint":false},{"year":2017,"finding":"Crystal structure of murine 4-1BB at 2.2 Å resolution reveals four cysteine-rich domains (CRDs) with CRD1 organization and CRD3/4 orientation distinct from other TNFRSFs. Two Asn residues within CRD4 are N-linked glycosylated and mediate m4-1BB binding to galectin-9 (Gal-9). Both N- and C-terminal domains of Gal-9 bind m4-1BB (with lower affinity than m4-1BBL). m4-1BBL forms a covalent dimer (via two cysteines absent in h4-1BBL), and since m4-1BBL can recruit only two m4-1BB monomers, Gal-9 is proposed to aid aggregation for efficient signaling.","method":"X-ray crystallography (sulfur-SAD phasing); surface plasmon resonance kinetics; glycosylation mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with binding kinetics; single lab but multiple orthogonal methods","pmids":["29242193"],"is_preprint":false},{"year":2005,"finding":"Recombinant human 4-1BBL (AviTag-4-1BBL) exists as a homotrimer with nanomolar affinity for 4-1BB (Kd ~1.2 nM vs. 55.2 nM for FLAG-4-1BBL). The single extracellular cysteine (Cys-51) can form a disulfide bond in both recombinant and physiologically expressed 4-1BBL. Mutation of Cys-51 does not affect trimerization but increases the dissociation rate from 4-1BB. Soluble trimeric 4-1BBL inhibits PBMC proliferation but does not costimulate purified T cells; crosslinking of two trimeric 4-1BBL molecules is the minimum step required to elicit costimulatory activity.","method":"Recombinant protein production; analytical ultracentrifugation/gel filtration for trimerization; surface plasmon resonance; T cell proliferation assays; site-directed mutagenesis (C51 mutant)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution, mutagenesis, binding kinetics, and functional assays in single study with multiple orthogonal methods","pmids":["16204238"],"is_preprint":false},{"year":2007,"finding":"4-1BBL on macrophage surfaces interacts with TLRs to sustain TNF production during late-phase (2–8 h post-LPS) TLR4 signaling. This 4-1BBL function is independent of its receptor 4-1BB and does not require MyD88 or TRIF adaptors. 4-1BBL does not affect early NF-κB activation but is required for late-phase activation of CREB and C/EBP transcription factors. Co-immunoprecipitation showed TLR4-MyD88 complexes form during the first hour, while TLR4-4-1BBL interactions form between 2 and 8 h after LPS.","method":"Co-immunoprecipitation; 4-1BBL-deficient macrophages (genetic ablation); reporter assays for NF-κB, CREB, C/EBP; cytokine ELISA","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with genetic KO validation, multiple transcription factor readouts, published in high-impact journal","pmids":["17496895"],"is_preprint":false},{"year":2013,"finding":"4-1BBL mediates late-phase TLR4 signaling by interacting with TIRAP and IRAK2. After TLR4 early signaling induces 4-1bbl expression, 4-1BBL translocates to the plasma membrane and forms a complex with TLR4. This TLR4-4-1BBL complex signals through TIRAP and IRAK2, which recruit the TRAF6/TAK1/TAB1 complex to sustain TNF-α production. Inhibition of this late-phase pathway reduced LPS-induced TNF-α production and ameliorated LPS-induced sepsis in mice.","method":"Co-immunoprecipitation; genetic knockouts (TIRAP-/-, IRAK2-/- mice); dominant-negative constructs; LPS-induced sepsis model; cytokine measurement","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP plus multiple genetic KO models; extends prior mechanistic finding (PMID 17496895) with pathway intermediates identified","pmids":["24084649"],"is_preprint":false},{"year":2011,"finding":"Reverse signaling through CD137L (4-1BBL) in tubular epithelial cells (TECs) is required for acute kidney ischemia-reperfusion injury (IRI). CD137 on NK cells engages CD137L on TECs, triggering CD137L reverse signaling that induces TEC production of CXCL1 and CXCL2, driving neutrophil recruitment and a proinflammatory cascade. Genetic experiments showed both CD137 on NK cells and CD137L on TECs are required for this process.","method":"Mouse IRI model; genetic knockouts (CD137-/-, CD137L-/- mice); cell-specific expression analysis; cytokine/chemokine measurement; neutrophil depletion","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — clean KO models with specific phenotypic readout and mechanistic chemokine identification","pmids":["22160719"],"is_preprint":false},{"year":2008,"finding":"4-1BB and 4-1BBL interactions suppress myelopoiesis: 4-1BBL is expressed on hematopoietic stem cells, common myeloid progenitors (CMPs), and granulocyte-macrophage progenitors (GMPs); 4-1BB is inducible on activated myeloid progenitors. Mice deficient in 4-1BB or 4-1BBL have increased steady-state numbers of GMPs, myeloid-lineage cells, and mature dendritic cells. Bone marrow chimeras and in vitro differentiation assays confirmed that the 4-1BBL on progenitors binds 4-1BB to inhibit myeloid and DC lineage differentiation.","method":"4-1BB-/- and 4-1BBL-/- mice; bone marrow chimeras; flow cytometry; in vitro differentiation assays","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO models replicated by bone marrow chimeras and in vitro assays, published in high-impact journal","pmids":["18604213"],"is_preprint":false},{"year":2007,"finding":"4-1BBL costimulation leads to TNFR-associated factor 1 (TRAF1)-dependent down-modulation of the pro-apoptotic molecule Bim in activated CD8 T cells. Reducing TRAF1 levels using siRNA resulted in increased Bim levels in 4-1BBL-stimulated T cells, demonstrating TRAF1 is required downstream of 4-1BBL signaling to suppress Bim and thereby increase T cell expansion.","method":"siRNA knockdown of TRAF1; intracellular Bim protein measurement; antigen-specific CD8 T cell expansion assays; flow cytometry","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA-mediated loss-of-function with specific molecular readout; single lab","pmids":["18056369"],"is_preprint":false},{"year":2009,"finding":"Reverse signaling of 4-1BBL into monocytes (triggered by anti-4-1BBL antibody) induces their differentiation into potent dendritic cells. This process involves nuclear translocation of NF-κB and requires autocrine signaling from GM-CSF, M-CSF, and Flt3 ligand, as neutralization of these factors inhibited proliferation. The resulting DCs exhibit a Th1-inducing phenotype with elevated IL-12 and IFN-γ and reduced IL-10.","method":"Anti-4-1BBL mAb stimulation; NF-κB nuclear translocation assay; neutralizing antibodies against GM-CSF, M-CSF, and Flt3L; cytokine ELISA; flow cytometry","journal":"International immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional readouts and mechanistic neutralization experiments; single lab","pmids":["19684160"],"is_preprint":false},{"year":2020,"finding":"4-1BBL signaling in macrophages is dependent on glycolysis for early TLR-induced 4-1BBL expression, and the sustained late-phase 4-1BBL-mediated inflammatory response depends on glycolysis and fatty acid synthesis. Genetic ablation or antibody blockade of 4-1BBL signaling alleviated imiquimod-induced psoriasis and regulated macrophage polarization in vitro. The psoriasis-promoting effect of 4-1BBL was independent of its receptor 4-1BB (4-1BB deficiency augmented psoriasis severity through different mechanisms).","method":"4-1BBL-/- and 4-1BB-/- mice; metabolic inhibitors (2-DG, cerulenin); anti-4-1BBL antibody; 4-1BB-Fc decoy; imiquimod psoriasis model; cytokine measurement","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO and pharmacologic inhibition with specific metabolic and phenotypic readouts; single lab","pmids":["32041783"],"is_preprint":false},{"year":2015,"finding":"4-1BBL signaling promotes macrophage/monocyte proliferation by reprogramming glucose metabolism via AKT-mTOR signaling. 4-1BBL stimulation increased glucose uptake, GLUT1 expression, glycolytic enzyme levels, lactate production, and transcription of pentose phosphate pathway and lipogenesis genes. 2-deoxyglucose (glycolytic inhibitor) completely abolished 4-1BBL-induced macrophage proliferation.","method":"4-1BBL stimulation on macrophages; glucose uptake assay; Western blot; qRT-PCR; metabolic inhibitor (2-DG); AKT-mTOR pathway analysis","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal metabolic readouts with pharmacologic inhibition; single lab","pmids":["25691217"],"is_preprint":false},{"year":2012,"finding":"4-1BB/4-1BBL interaction promotes bidirectional inflammatory signaling in adipocytes and macrophages. 4-1BB is expressed on adipocytes and upregulated by obesity-related factors, which also enhance 4-1BBL expression on macrophages. 4-1BB and/or 4-1BBL agonists activated MAPK/IκBα and MAPK/Akt signaling in adipocytes and macrophages respectively, and enhanced inflammatory cytokine release (MCP-1, TNF-α, IL-6). Disruption of 4-1BB/4-1BBL interaction in contact co-culture decreased inflammatory cytokine release.","method":"Co-culture of adipocytes and macrophages; 4-1BB/4-1BBL agonists; signaling pathway (MAPK, Akt, IκBα) analysis; cytokine ELISA; blocking antibodies","journal":"Mediators of inflammation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based co-culture with signaling pathway analysis and blocking experiments; single lab","pmids":["23316108"],"is_preprint":false},{"year":1999,"finding":"4-1BBL-/- mice exhibit a weaker CTL response to influenza virus compared to wild-type, while the CTL response to LCMV is normal. 4-1BBL-/-CD28-/- mice show a delay in skin allograft rejection and respond poorly to influenza. CD28-/- T cells show substantially inhibited allogeneic CTL responses to 4-1BBL-expressing APC (blocked by soluble 4-1BB receptor). TCR-transgenic CD28-/- T cells are responsive to 4-1BBL co-stimulation when a suboptimal agonist peptide is used but not with the wild-type peptide, placing 4-1BBL as a co-stimulator that augments suboptimal CTL responses.","method":"4-1BBL-/- and 4-1BBL-/-CD28-/- mice; viral infection models (influenza, LCMV); skin allograft rejection; soluble 4-1BB receptor blocking; CTL assays; TCR-transgenic CD28-/- T cells","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic KO models with multiple immune challenge readouts; independently informative epistasis","pmids":["10528184"],"is_preprint":false},{"year":2022,"finding":"Leukemic extracellular vesicles (EVs) shuttle 4-1BBL/CD137L on their surface to promote suppressive effector regulatory T cells (Tregs). 4-1BBL on leukemic EVs promoted suppressive activity and effector phenotype of Tregs by regulating expression of CD30 and TNFR2. Leukemic EV secretion is Rab27a-dependent.","method":"Leukemic EV isolation; flow cytometry; Rab27a-deficient mouse model; Treg functional assays; transcriptomic profiling","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic (Rab27a KO) and functional EV experiments; single lab","pmids":["35130345"],"is_preprint":false},{"year":2022,"finding":"A homozygous missense mutation (p.V140G) in TNFSF9 (CD137L/4-1BBL) causes a loss-of-function with absent surface expression of CD137L on patient monocytes, dendritic cells, and EBV-infected B cells. Patient EBV-infected B cells failed to trigger expansion of EBV-specific T cells. T cell expansion was recovered when CD137L expression was restored on patient B cells, demonstrating that CD137L is required for CD137-mediated co-stimulation supporting EBV-specific T cell responses.","method":"Patient genetics (homozygous TNFSF9 missense mutation); ectopic expression of wild-type vs. mutant CD137L in HEK and P815 cells; flow cytometry; EBV-specific T cell expansion assays; rescue by CD137L restoration","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — natural human loss-of-function mutation with rescue experiment; direct causal link between CD137L and EBV-specific T cell expansion","pmids":["35657354"],"is_preprint":false},{"year":1997,"finding":"m4-1BBL binding to m4-1BB blocks laminin (LN) binding, whereas m4-1BB binding to LN does not block m4-1BBL binding. Truncation studies showed regions downstream of the LN-homologous domain participate in LN binding, and the intact protein is required for m4-1BBL binding. Human 4-1BB does not bind ECM proteins, only h4-1BBL, indicating this ECM-binding property is not conserved across species.","method":"Binding competition assays; truncated protein fragments; anti-4-1BB monoclonal antibody blocking panel; murine/human chimeras","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple binding competition and domain-mapping experiments; single lab","pmids":["9045669"],"is_preprint":false},{"year":2008,"finding":"The scFv36-4-1BBL fusion protein (scFv against FAP fused to 4-1BBL extracellular domain) forms a homotrimeric molecule that binds FAP and 4-1BB simultaneously. T cell costimulation (measured by IFN-γ release) was concentration-dependent, ligand-specific, and substantially constrained to FAP-expressing target cells, demonstrating that targeted presentation of 4-1BBL is required for its co-stimulatory activity.","method":"Recombinant fusion protein generation; binding assays to FAP and 4-1BB; co-culture T cell costimulation assay; IFN-γ ELISA","journal":"Journal of immunotherapy (Hagerstown, Md. : 1997)","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — functional in vitro assays confirming that 4-1BBL trimeric presentation is required for activity; single lab","pmids":["18779748"],"is_preprint":false},{"year":2015,"finding":"Tumor cell-derived soluble CD137 (sCD137), produced under hypoxic conditions via alternative splicing lacking the transmembrane domain, binds CD137L (4-1BBL) on APCs and prevents interaction of CD137L with transmembrane CD137 on T cells, thereby blocking T cell co-stimulation. shRNA silencing of CD137 in tumor cells rendered tumors more immunogenic in immunocompetent mice but not in immunodeficient or CD8+ T cell-depleted mice.","method":"Hypoxia exposure of tumor cell lines; RT-PCR for splice variants; ELISA for sCD137; T cell co-culture with CD137L transfectants; shRNA knockdown; in vivo tumor immunogenicity assays","journal":"Oncoimmunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic co-culture blocking assay with in vivo genetic validation; single lab","pmids":["26942078"],"is_preprint":false},{"year":2003,"finding":"Anti-4-1BBL monoclonal antibody (1F1) triggers reverse signaling through 4-1BBL on monocytes, inducing monocyte proliferation from peripheral blood. The same antibody inhibited T lymphocyte proliferation costimulated by soluble 4-1BBL and anti-CD3.","method":"Anti-4-1BBL mAb generation; flow cytometry; Western blotting; T cell proliferation inhibition assay; monocyte proliferation assay","journal":"Hybridoma and hybridomics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single antibody-based activation experiment; single lab; no downstream signaling identified","pmids":["14678652"],"is_preprint":false},{"year":2008,"finding":"CD137L-mediated reverse signaling inhibits RANKL-induced osteoclast formation in a dose-dependent manner. Cross-linking of CD137L with anti-CD137L mAb inhibited M-CSF/RANKL-evoked formation of multi-nucleated osteoclasts from bone marrow cells.","method":"Anti-CD137L mAb crosslinking; osteoclastogenesis assay from murine bone marrow and RAW264.7 cells; RANKL/M-CSF stimulation","journal":"Immunobiology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single antibody-based activation assay; no downstream signaling identified; single lab","pmids":["19167994"],"is_preprint":false},{"year":2015,"finding":"miR-484 directly represses CD137L (TNFSF9) expression in MSI colorectal cancer cells. Loss of miR-484 via CpG island methylation leads to increased CD137L expression, which promotes IL-8 production by MSI CRC cells.","method":"miRNA microarray; qRT-PCR; CpG methylation analysis; miR-484 overexpression/inhibition; CD137L expression measurement; IL-8 ELISA","journal":"The Journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct functional link between miR-484, CD137L, and IL-8 in matched in vitro and in vivo experiments; single lab","pmids":["25727216"],"is_preprint":false},{"year":2017,"finding":"CD137-CD137L signaling promotes vascular smooth muscle cell (VSMC) phenotype transformation from contractile to synthetic via NFATc1 activation. Recombinant CD137L upregulated NFATc1 expression; contractile phenotype markers (SM-MHC, α-SMA) decreased while synthetic marker (vimentin) and cell migration increased. These effects were blocked by anti-CD137 antibody or NFATc1 siRNA, and NFATc1 overexpression alone caused phenotype transformation.","method":"Recombinant CD137L stimulation; NFATc1 siRNA and lentiviral overexpression; Western blot; immunofluorescence; Transwell migration assay; in vivo neointima model","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA and overexpression with in vitro and in vivo validation; single lab","pmids":["28770466"],"is_preprint":false},{"year":2024,"finding":"4-1BBL expressed on Batf3-lineage dendritic cells within the tumor microenvironment is a major positive co-stimulatory signal for CD8+ T cell reinvigoration and tumor regression in response to PD-1/PD-L1 blockade. Blocking 4-1BBL or depleting Batf3+ DCs abrogated the efficacy of anti-PD-1 therapy.","method":"Gene-targeted mice (Batf3-/-); anti-4-1BBL blocking antibodies; flow cytometry; spatial transcriptomics on human tumor samples; tumor regression readout","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and antibody-blocking models with spatial validation in human tumors; single lab","pmids":["38656869"],"is_preprint":false},{"year":2023,"finding":"Macrophage STING signaling activates NLRP3-mediated IL-18 and IL-1β production, which promotes 4-1BBL expression on macrophages and 4-1BB expression on NK cells respectively, enabling 4-1BBL/4-1BB co-stimulation that enhances NK cell antitumor function against colorectal cancer liver metastasis.","method":"Global and myeloid-specific STING-/- mice; myeloid NLRP3-/- mice; NK cell depletion; bone marrow-derived macrophage/NK co-culture; flow cytometry; intrasplenic CRC mouse model","journal":"Journal for immunotherapy of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple genetic KO models with epistasis analysis; single lab","pmids":["36927529"],"is_preprint":false},{"year":2022,"finding":"Galectin-3 (Gal-3) binds to both soluble and membrane-bound 4-1BB without blocking co-binding of 4-1BBL. Gal-3 forms large soluble 4-1BB/Gal-3 complexes (>100 nm) in plasma that attach to membrane 4-1BB on T cells, resulting in a ~4-fold decrease in TNFα production by 4-1BB+Gal-3+ T cells after 4-1BBL exposure, demonstrating Gal-3 suppresses 4-1BBL bioactivity by receptor clustering rather than direct competition.","method":"Co-binding assays; particle size analysis (plasma complexes); flow cytometry; TNFα production assay; 4-1BB-transfected HEK293 cells","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal binding and functional assays; single lab","pmids":["35812455"],"is_preprint":false},{"year":2024,"finding":"Hypoxia-induced lactic acid accumulation in glioma cells is absorbed by macrophages via MCT-1, leading to H3K18 lactylation (H3K18La) that epigenetically upregulates TNFSF9 expression. Elevated macrophage TNFSF9 then promotes M2 macrophage polarization and facilitates glioma progression. ChIP-seq identified H3K18La enrichment at the TNFSF9 locus. Silencing MCT-1 or the glycolysis inhibitor reversed TNFSF9 upregulation and M2 polarization.","method":"ChIP-seq for H3K18La; MCT-1 siRNA knockdown; glycolysis inhibitor; TNFSF9 knockdown; in vitro and in vivo glioma models","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-seq plus genetic and pharmacologic perturbations in vitro and in vivo; single lab","pmids":["39010835"],"is_preprint":false},{"year":2022,"finding":"CD137L released by macrophages (stimulated by VEGF-C) binds to CD137 on lymphatic endothelial cells (LECs), activating PI3K/AKT/mTOR signaling that promotes autophagy (LC3-I to LC3-II conversion, Atg5, Atg7, Atg12 upregulation) and thereby enhances LEC proliferation, migration, and tube formation. Knockdown of Atg5 or Atg7 blocked CD137L-induced autophagy and lymphangiogenesis.","method":"Recombinant CD137L treatment of LECs; CD137 siRNA knockdown; Western blot (LC3, Atg proteins); PI3K/AKT/mTOR pathway analysis; Atg5/Atg7 siRNA; LEC proliferation/migration/tube formation assays; UUO mouse model","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple siRNA knockdowns with signaling pathway and functional readouts; single lab","pmids":["35173546"],"is_preprint":false},{"year":2012,"finding":"SA-4-1BBL (oligomeric 4-1BBL) costimulation inhibits TGF-β- and antigen-driven conversion of naïve CD4+FoxP3- T cells into induced Tregs via stimulation of IFN-γ production by CD4+FoxP3- T cells. SA-4-1BBL also blocked conversion of CD4+ T cells into Tregs by EG.7 tumors in vivo.","method":"IFN-γ neutralization; in vitro iTreg conversion assay; in vivo tumor model with SA-4-1BBL treatment; FoxP3 expression analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic IFN-γ neutralization experiment with in vitro and in vivo validation; single lab","pmids":["22870329"],"is_preprint":false}],"current_model":"TNFSF9 (4-1BBL/CD137L) is a trimeric TNF superfamily ligand that binds its cognate receptor 4-1BB (CD137) at the inter-protomer crevice via a distinct mechanism; crosslinking of trimeric 4-1BBL is required for co-stimulatory activity, and human 4-1BB can form CRD4 disulfide-linked dimers that amplify signaling through receptor network formation. Beyond forward 4-1BB signaling on T, NK, and myeloid cells—which promotes T cell survival via TRAF1-dependent Bim downregulation, suppresses Treg conversion via IFN-γ, and inhibits myelopoiesis—4-1BBL also transduces receptor-independent reverse signals into the cells that express it: in macrophages, it interacts with TLR4 (recruiting TIRAP/IRAK2/TRAF6/TAK1) to sustain late-phase CREB/C-EBP-dependent TNF production and regulates macrophage polarization and metabolic reprogramming via AKT-mTOR; in epithelial cells, CD137-driven CD137L reverse signaling induces CXCL1/CXCL2 secretion to recruit neutrophils during ischemia-reperfusion injury; and in monocytes, CD137L reverse signaling drives NF-κB-dependent differentiation into inflammatory dendritic cells. Structural studies confirm the canonical bell-shaped trimeric assembly of 4-1BBL in complex with 4-1BB, with important species differences between mouse (covalent dimer, GH-loop–mediated binding) and human (non-covalent trimer, distinct binding geometry) molecules, and galectin-9 or galectin-3 can modulate 4-1BB receptor clustering and signaling amplitude."},"narrative":{"mechanistic_narrative":"TNFSF9 (4-1BBL/CD137L) is a trimeric TNF-superfamily ligand that serves as a bidirectional immune co-stimulator, transmitting forward signals through its receptor 4-1BB (CD137) and receptor-independent reverse signals into the cells that express it [PMID:30410017, PMID:17496895]. Structurally, human 4-1BBL assembles as a canonical bell-shaped trimer and engages 4-1BB predominantly at one protomer via the inter-protomer crevice using a non-canonical mechanism lacking the typical DE-loop tyrosine contact; human 4-1BB additionally forms CRD4 disulfide-linked dimers that crosslink complexes into a 2D network to amplify signaling [PMID:30410017, PMID:29720398, PMID:29720399]. Mouse 4-1BBL diverges as a covalent disulfide-linked dimer that binds via the GH loop, a species difference proposed to be compensated by galectin-9-mediated receptor aggregation [PMID:30545939, PMID:29242193]. Soluble trimeric 4-1BBL alone is insufficient for co-stimulation; crosslinking of two trimers or targeted surface presentation is the minimal requirement for co-stimulatory activity [PMID:16204238, PMID:18779748]. Through forward signaling, 4-1BBL augments suboptimal CTL responses [PMID:10528184], drives TRAF1-dependent downregulation of pro-apoptotic Bim to promote CD8 T cell expansion [PMID:18056369], suppresses TGF-β-driven Treg conversion via IFN-γ [PMID:22870329], and restrains myelopoiesis and dendritic cell differentiation [PMID:18604213]. In its reverse-signaling capacity, surface 4-1BBL on macrophages forms a complex with TLR4 that recruits TIRAP, IRAK2 and the TRAF6/TAK1/TAB1 module to sustain late-phase CREB/C-EBP-dependent TNF production independent of 4-1BB, MyD88 and TRIF [PMID:17496895, PMID:24084649], and reprograms macrophage glucose metabolism through AKT-mTOR to support proliferation and inflammation [PMID:32041783, PMID:25691217]. Reverse signaling also induces CXCL1/CXCL2-driven neutrophil recruitment in epithelial cells during ischemia-reperfusion injury [PMID:22160719] and NF-κB-dependent monocyte differentiation into inflammatory dendritic cells [PMID:19684160]. A homozygous TNFSF9 missense mutation (p.V140G) abolishing surface CD137L causes loss of 4-1BB-mediated co-stimulation and failure of EBV-specific T cell expansion, with rescue upon restoring CD137L [PMID:35657354].","teleology":[{"year":1997,"claim":"Established that 4-1BBL/4-1BB binding involves species-specific properties, with murine 4-1BB binding ECM laminin in a manner mutually exclusive with ligand, a feature not conserved in human.","evidence":"Binding competition and domain-mapping with truncated fragments and murine/human chimeras","pmids":["9045669"],"confidence":"Medium","gaps":["No structural basis for the species difference resolved at this stage","Functional consequence of laminin binding in vivo not established"]},{"year":1999,"claim":"Defined 4-1BBL as a co-stimulator that augments suboptimal CTL responses, separable from CD28, by showing genetic deficiency impairs antiviral and allograft responses.","evidence":"4-1BBL-/- and 4-1BBL-/-CD28-/- mice across influenza, LCMV, and allograft models with soluble receptor blocking","pmids":["10528184"],"confidence":"High","gaps":["Downstream signaling intermediates not identified","Antigen-strength dependence mechanism unexplained"]},{"year":2005,"claim":"Resolved the oligomeric requirement for co-stimulation, showing soluble trimeric ligand is insufficient and crosslinking of two trimers is the minimal activating step.","evidence":"Recombinant 4-1BBL, ultracentrifugation/gel filtration, SPR, C51 mutagenesis, and T cell proliferation assays","pmids":["16204238"],"confidence":"High","gaps":["Physiological crosslinking mechanism on cell surfaces not defined","Role of Cys-51 disulfide in vivo unclear"]},{"year":2007,"claim":"Identified a receptor-independent reverse-signaling function: surface 4-1BBL on macrophages associates with TLR4 to sustain late-phase TNF production via CREB/C-EBP, independent of MyD88/TRIF.","evidence":"Reciprocal Co-IP, 4-1BBL-deficient macrophages, and NF-κB/CREB/C-EBP reporter and cytokine assays","pmids":["17496895"],"confidence":"High","gaps":["Adaptors bridging TLR4-4-1BBL not yet identified","How early signaling triggers ligand translocation unknown"]},{"year":2007,"claim":"Defined a forward signaling effector: 4-1BBL co-stimulation downregulates pro-apoptotic Bim via TRAF1 to promote CD8 T cell survival.","evidence":"TRAF1 siRNA knockdown with intracellular Bim measurement and antigen-specific CD8 expansion assays","pmids":["18056369"],"confidence":"Medium","gaps":["Single-lab siRNA loss-of-function","Link between TRAF1 and Bim regulation mechanistically incomplete"]},{"year":2008,"claim":"Showed 4-1BBL forward signaling restrains myelopoiesis and DC differentiation at the progenitor level.","evidence":"4-1BB-/- and 4-1BBL-/- mice, bone marrow chimeras, and in vitro differentiation assays","pmids":["18604213"],"confidence":"High","gaps":["Intracellular signaling controlling progenitor inhibition not defined"]},{"year":2009,"claim":"Extended reverse signaling to monocytes, showing 4-1BBL engagement drives NF-κB-dependent differentiation into Th1-inducing dendritic cells.","evidence":"Anti-4-1BBL mAb stimulation, NF-κB nuclear translocation, and cytokine neutralization (GM-CSF/M-CSF/Flt3L)","pmids":["19684160"],"confidence":"Medium","gaps":["Antibody-driven rather than physiological ligand engagement","Proximal signaling components linking ligand to NF-κB unidentified"]},{"year":2011,"claim":"Demonstrated reverse signaling drives tissue pathology: CD137 on NK cells engages epithelial CD137L to induce CXCL1/CXCL2 and neutrophil recruitment in kidney ischemia-reperfusion injury.","evidence":"CD137-/- and CD137L-/- mice in an IRI model with chemokine measurement and neutrophil depletion","pmids":["22160719"],"confidence":"High","gaps":["Intracellular reverse-signaling cascade in epithelial cells not mapped"]},{"year":2013,"claim":"Identified the molecular intermediates of macrophage reverse signaling, placing TIRAP and IRAK2 between the TLR4-4-1BBL complex and TRAF6/TAK1-driven sustained TNF.","evidence":"Co-IP, TIRAP-/- and IRAK2-/- mice, dominant-negative constructs, and an LPS sepsis model","pmids":["24084649"],"confidence":"High","gaps":["Structural basis of the TLR4-4-1BBL interaction unknown","How 4-1BBL recruits TIRAP/IRAK2 mechanistically unclear"]},{"year":2012,"claim":"Showed 4-1BBL forward co-stimulation blocks induced Treg conversion through IFN-γ.","evidence":"SA-4-1BBL oligomer, IFN-γ neutralization, in vitro iTreg conversion, and an in vivo tumor model","pmids":["22870329"],"confidence":"Medium","gaps":["Single-lab; uses engineered oligomeric ligand","Direct vs indirect IFN-γ contribution not fully separated"]},{"year":2012,"claim":"Extended bidirectional signaling to metabolic inflammation, with 4-1BB/4-1BBL contact between adipocytes and macrophages activating MAPK/Akt/IκBα and inflammatory cytokine release.","evidence":"Adipocyte-macrophage co-culture, agonists, signaling analysis, and blocking antibodies","pmids":["23316108"],"confidence":"Medium","gaps":["Forward vs reverse signaling contributions not disentangled","Single-lab co-culture system"]},{"year":2015,"claim":"Defined the metabolic basis of reverse signaling, showing 4-1BBL reprograms glucose metabolism via AKT-mTOR to drive macrophage proliferation.","evidence":"4-1BBL stimulation, glucose uptake assays, GLUT1/glycolytic enzyme analysis, and 2-DG inhibition","pmids":["25691217"],"confidence":"Medium","gaps":["Receptor-independence not formally controlled in this study","Single-lab metabolic readouts"]},{"year":2015,"claim":"Identified a soluble decoy mechanism, where hypoxia-induced soluble CD137 binds CD137L on APCs and blocks T cell co-stimulation, promoting tumor immune escape.","evidence":"Hypoxia, splice-variant RT-PCR, ELISA, T cell co-culture blocking, shRNA, and in vivo tumor immunogenicity","pmids":["26942078"],"confidence":"Medium","gaps":["Single-lab; physiological abundance of sCD137 in human tumors not quantified"]},{"year":2015,"claim":"Connected TNFSF9 expression to epigenetic/post-transcriptional control, with miR-484 loss via CpG methylation derepressing CD137L to promote IL-8 in MSI colorectal cancer.","evidence":"miRNA microarray, methylation analysis, miR-484 gain/loss, and IL-8 measurement","pmids":["25727216"],"confidence":"Medium","gaps":["Direct miR-484-TNFSF9 binding interaction confirmation limited to single lab"]},{"year":2017,"claim":"Showed CD137-CD137L signaling drives vascular smooth muscle phenotype switching through NFATc1 activation.","evidence":"Recombinant CD137L, NFATc1 siRNA/overexpression, migration assays, and an in vivo neointima model","pmids":["28770466"],"confidence":"Medium","gaps":["Forward vs reverse signaling directionality not resolved","Single-lab"]},{"year":2017,"claim":"Provided structural detail of the murine receptor, revealing distinct CRD organization and CRD4 N-glycans that mediate galectin-9 binding, supporting a model where galectin-9 aids aggregation of the dimeric mouse system.","evidence":"X-ray crystallography of m4-1BB, SPR kinetics, and glycosylation mapping","pmids":["29242193"],"confidence":"High","gaps":["Functional role of galectin-9 aggregation in signaling not directly tested in vivo"]},{"year":2018,"claim":"Resolved the long-disputed ligand architecture, establishing the human 4-1BBL bell-shaped trimer and a non-canonical inter-protomer binding mode, and defining how receptor CRD4 disulfide dimers amplify signaling.","evidence":"Multiple independent crystal structures of complex, free ligand, and antibody-bound receptor, with mutagenesis and cell-based agonist assays","pmids":["30410017","29720398","29720399"],"confidence":"High","gaps":["Dynamics of 2D network formation on living cell surfaces not directly visualized"]},{"year":2018,"claim":"Clarified the species divergence in ligand assembly, defining mouse 4-1BBL as a covalent dimer with GH-loop-mediated receptor selectivity.","evidence":"Crystal structures of free and complexed m4-1BBL with structure-guided interface mutagenesis","pmids":["30545939"],"confidence":"High","gaps":["How the dimeric mouse geometry achieves productive clustering not fully resolved without galectin contribution"]},{"year":2022,"claim":"Provided definitive human causal genetics, showing a homozygous TNFSF9 loss-of-function mutation abolishes CD137L surface expression and EBV-specific T cell expansion, rescued by CD137L restoration.","evidence":"Patient genetics, ectopic wild-type vs mutant expression, and rescue of EBV-specific T cell expansion","pmids":["35657354"],"confidence":"High","gaps":["Full clinical spectrum of TNFSF9 deficiency beyond EBV immunity not delineated"]},{"year":2022,"claim":"Identified galectin-3 as a modulator that suppresses 4-1BBL bioactivity by clustering receptor into large complexes rather than competing for binding.","evidence":"Co-binding assays, plasma particle sizing, flow cytometry, and TNFα production on 4-1BB-transfected cells","pmids":["35812455"],"confidence":"Medium","gaps":["In vivo relevance of galectin-3 modulation not established","Single-lab"]},{"year":2022,"claim":"Showed leukemic extracellular vesicles can deliver surface 4-1BBL to promote suppressive effector Tregs, expanding the modes of ligand presentation.","evidence":"Leukemic EV isolation, Rab27a-deficient mice, Treg functional assays, and transcriptomics","pmids":["35130345"],"confidence":"Medium","gaps":["Whether vesicular 4-1BBL signals forward, reverse, or both not separated","Single-lab"]},{"year":2022,"claim":"Extended reverse-signaling-like activity to lymphangiogenesis, with macrophage-derived CD137L activating CD137 on lymphatic endothelial cells to drive PI3K/AKT/mTOR-dependent autophagy.","evidence":"Recombinant CD137L, CD137 and Atg5/Atg7 siRNA, pathway analysis, functional LEC assays, and a UUO model","pmids":["35173546"],"confidence":"Medium","gaps":["Single-lab; receptor-side signaling rather than ligand reverse signaling"]},{"year":2023,"claim":"Placed 4-1BBL within an innate-to-NK co-stimulatory axis, where macrophage STING-NLRP3 signaling induces 4-1BBL to enhance NK antitumor function.","evidence":"STING-/- and NLRP3-/- mice, NK depletion, macrophage/NK co-culture, and a CRC liver metastasis model","pmids":["36927529"],"confidence":"Medium","gaps":["Single-lab; direct contribution of 4-1BBL versus IL-18/IL-1β partly inferred"]},{"year":2024,"claim":"Defined 4-1BBL on Batf3-lineage dendritic cells as a major co-stimulatory signal required for CD8 T cell reinvigoration during PD-1/PD-L1 blockade.","evidence":"Batf3-/- mice, anti-4-1BBL blocking, flow cytometry, and spatial transcriptomics on human tumors","pmids":["38656869"],"confidence":"Medium","gaps":["Single-lab; molecular determinants of DC-restricted ligand activity not detailed"]},{"year":2024,"claim":"Linked tumor metabolism to TNFSF9 transcription, showing glioma-derived lactate drives macrophage H3K18 lactylation that upregulates TNFSF9 and promotes M2 polarization.","evidence":"ChIP-seq for H3K18La, MCT-1 and TNFSF9 knockdown, glycolysis inhibition, and in vivo glioma models","pmids":["39010835"],"confidence":"Medium","gaps":["Single-lab; whether the M2 effect requires 4-1BBL signaling versus correlated expression not fully separated"]},{"year":null,"claim":"How the same trimeric ligand selects between forward co-stimulation and distinct reverse-signaling cascades in different cell types, and the structural/adaptor basis for assembling the reverse-signaling TLR4-4-1BBL-TIRAP-IRAK2 platform, remain unresolved.","evidence":"No timeline discovery resolves the molecular switch governing forward versus reverse signaling or the structure of the reverse-signaling complex","pmids":[],"confidence":"Low","gaps":["No structure of the 4-1BBL reverse-signaling complex with TLR4/TIRAP/IRAK2","Cytoplasmic determinants of 4-1BBL reverse signaling not mapped","Mechanism partitioning forward versus reverse signaling per cell type unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,4,14,18]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[5,6,7,10]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,2]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,6,4]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[15,19]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5,8,14,24]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,9,12,28]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[11,12,27]}],"complexes":[],"partners":["TNFRSF9","TLR4","TIRAP","IRAK2","TRAF1","LGALS9","LGALS3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P41273","full_name":"Tumor necrosis factor ligand superfamily member 9","aliases":["4-1BB ligand","4-1BBL"],"length_aa":254,"mass_kda":26.6,"function":"Cytokine that binds to TNFRSF9. Induces the proliferation of activated peripheral blood T-cells. May have a role in activation-induced cell death (AICD). May play a role in cognate interactions between T-cells and B-cells/macrophages","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/P41273/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TNFSF9","classification":"Not Classified","n_dependent_lines":6,"n_total_lines":1208,"dependency_fraction":0.004966887417218543},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TNFSF9","total_profiled":1310},"omim":[{"mim_id":"620282","title":"IMMUNODEFICIENCY 109 WITH LYMPHOPROLIFERATION; IMD109","url":"https://www.omim.org/entry/620282"},{"mim_id":"610424","title":"HEPATITIS B VIRUS, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/610424"},{"mim_id":"606182","title":"TUMOR NECROSIS FACTOR LIGAND SUPERFAMILY, MEMBER 9; TNFSF9","url":"https://www.omim.org/entry/606182"},{"mim_id":"604520","title":"TUMOR NECROSIS FACTOR LIGAND SUPERFAMILY, MEMBER 14; TNFSF14","url":"https://www.omim.org/entry/604520"},{"mim_id":"603594","title":"TUMOR NECROSIS FACTOR LIGAND SUPERFAMILY, MEMBER 4; TNFSF4","url":"https://www.omim.org/entry/603594"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"esophagus","ntpm":9.6},{"tissue":"vagina","ntpm":9.1}],"url":"https://www.proteinatlas.org/search/TNFSF9"},"hgnc":{"alias_symbol":["4-1BB-L","4-1BBL","CD137L"],"prev_symbol":[]},"alphafold":{"accession":"P41273","domains":[{"cath_id":"2.60.120.40","chopping":"87-238","consensus_level":"medium","plddt":91.1037,"start":87,"end":238}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P41273","model_url":"https://alphafold.ebi.ac.uk/files/AF-P41273-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P41273-F1-predicted_aligned_error_v6.png","plddt_mean":76.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TNFSF9","jax_strain_url":"https://www.jax.org/strain/search?query=TNFSF9"},"sequence":{"accession":"P41273","fasta_url":"https://rest.uniprot.org/uniprotkb/P41273.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P41273/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P41273"}},"corpus_meta":[{"pmid":"19426223","id":"PMC_19426223","title":"Immune 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human 4-1BB/4-1BBL complex, unbound 4-1BBL, and 4-1BB bound to utomilumab or urelumab were solved, revealing: (1) 4-1BBL forms a canonical bell-shaped trimer (not the previously reported three-bladed propeller), (2) 4-1BB binds predominantly to one protomer of the 4-1BBL trimer at the inter-protomer crevice via a distinct mechanism lacking the canonical DE-loop tyrosine interaction, (3) utomilumab binds 4-1BB CRDs 3–4 and blocks ligand, whereas urelumab binds CRD-1 away from the ligand-binding site, and (4) cell-based assays show utomilumab is a milder agonist than urelumab.\",\n      \"method\": \"X-ray crystallography (structures of complex, ligand alone, and antibody-bound receptor); cell-based functional assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple crystal structures with functional validation, replicated by two independent structural studies published simultaneously (PMIDs 30410017, 29720398, 29720399)\",\n      \"pmids\": [\"30410017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structure of the human 4-1BB/4-1BBL complex at 2.4 Å resolution shows 4-1BBL adopts a canonical bell-shaped trimer (contradicting a previously published propeller structure). Mutational data support this structure as biologically relevant. 4-1BB forms a disulfide-linked dimer via a CRD4 cysteine, and this covalent receptor dimerization can cross-link ligand-receptor complexes into a 2D signaling network, amplifying 4-1BB signaling.\",\n      \"method\": \"X-ray crystallography; site-directed mutagenesis; structural comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — independent crystal structure with mutagenesis, corroborated by PMID 30410017 published simultaneously\",\n      \"pmids\": [\"29720398\", \"29720399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structure of mouse 4-1BBL reveals a disulfide-linked dimeric assembly (unlike trimeric human 4-1BBL), mediated by Cys-246 and Ser-256 unique to m4-1BBL. Upon m4-1BB binding, m4-1BBL undergoes structural changes within each protomer and inter-subunit rotation. Each receptor monomer binds a single ligand subunit via CRD1, CRD2, and CRD3, with the GH loop (not DE loop) providing energetically critical contacts defining receptor selectivity.\",\n      \"method\": \"X-ray crystallography; structure-guided mutagenesis of binding interface\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures of free and complexed m4-1BBL with mutagenesis validation\",\n      \"pmids\": [\"30545939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of murine 4-1BB at 2.2 Å resolution reveals four cysteine-rich domains (CRDs) with CRD1 organization and CRD3/4 orientation distinct from other TNFRSFs. Two Asn residues within CRD4 are N-linked glycosylated and mediate m4-1BB binding to galectin-9 (Gal-9). Both N- and C-terminal domains of Gal-9 bind m4-1BB (with lower affinity than m4-1BBL). m4-1BBL forms a covalent dimer (via two cysteines absent in h4-1BBL), and since m4-1BBL can recruit only two m4-1BB monomers, Gal-9 is proposed to aid aggregation for efficient signaling.\",\n      \"method\": \"X-ray crystallography (sulfur-SAD phasing); surface plasmon resonance kinetics; glycosylation mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with binding kinetics; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"29242193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Recombinant human 4-1BBL (AviTag-4-1BBL) exists as a homotrimer with nanomolar affinity for 4-1BB (Kd ~1.2 nM vs. 55.2 nM for FLAG-4-1BBL). The single extracellular cysteine (Cys-51) can form a disulfide bond in both recombinant and physiologically expressed 4-1BBL. Mutation of Cys-51 does not affect trimerization but increases the dissociation rate from 4-1BB. Soluble trimeric 4-1BBL inhibits PBMC proliferation but does not costimulate purified T cells; crosslinking of two trimeric 4-1BBL molecules is the minimum step required to elicit costimulatory activity.\",\n      \"method\": \"Recombinant protein production; analytical ultracentrifugation/gel filtration for trimerization; surface plasmon resonance; T cell proliferation assays; site-directed mutagenesis (C51 mutant)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution, mutagenesis, binding kinetics, and functional assays in single study with multiple orthogonal methods\",\n      \"pmids\": [\"16204238\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"4-1BBL on macrophage surfaces interacts with TLRs to sustain TNF production during late-phase (2–8 h post-LPS) TLR4 signaling. This 4-1BBL function is independent of its receptor 4-1BB and does not require MyD88 or TRIF adaptors. 4-1BBL does not affect early NF-κB activation but is required for late-phase activation of CREB and C/EBP transcription factors. Co-immunoprecipitation showed TLR4-MyD88 complexes form during the first hour, while TLR4-4-1BBL interactions form between 2 and 8 h after LPS.\",\n      \"method\": \"Co-immunoprecipitation; 4-1BBL-deficient macrophages (genetic ablation); reporter assays for NF-κB, CREB, C/EBP; cytokine ELISA\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with genetic KO validation, multiple transcription factor readouts, published in high-impact journal\",\n      \"pmids\": [\"17496895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"4-1BBL mediates late-phase TLR4 signaling by interacting with TIRAP and IRAK2. After TLR4 early signaling induces 4-1bbl expression, 4-1BBL translocates to the plasma membrane and forms a complex with TLR4. This TLR4-4-1BBL complex signals through TIRAP and IRAK2, which recruit the TRAF6/TAK1/TAB1 complex to sustain TNF-α production. Inhibition of this late-phase pathway reduced LPS-induced TNF-α production and ameliorated LPS-induced sepsis in mice.\",\n      \"method\": \"Co-immunoprecipitation; genetic knockouts (TIRAP-/-, IRAK2-/- mice); dominant-negative constructs; LPS-induced sepsis model; cytokine measurement\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP plus multiple genetic KO models; extends prior mechanistic finding (PMID 17496895) with pathway intermediates identified\",\n      \"pmids\": [\"24084649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Reverse signaling through CD137L (4-1BBL) in tubular epithelial cells (TECs) is required for acute kidney ischemia-reperfusion injury (IRI). CD137 on NK cells engages CD137L on TECs, triggering CD137L reverse signaling that induces TEC production of CXCL1 and CXCL2, driving neutrophil recruitment and a proinflammatory cascade. Genetic experiments showed both CD137 on NK cells and CD137L on TECs are required for this process.\",\n      \"method\": \"Mouse IRI model; genetic knockouts (CD137-/-, CD137L-/- mice); cell-specific expression analysis; cytokine/chemokine measurement; neutrophil depletion\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO models with specific phenotypic readout and mechanistic chemokine identification\",\n      \"pmids\": [\"22160719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"4-1BB and 4-1BBL interactions suppress myelopoiesis: 4-1BBL is expressed on hematopoietic stem cells, common myeloid progenitors (CMPs), and granulocyte-macrophage progenitors (GMPs); 4-1BB is inducible on activated myeloid progenitors. Mice deficient in 4-1BB or 4-1BBL have increased steady-state numbers of GMPs, myeloid-lineage cells, and mature dendritic cells. Bone marrow chimeras and in vitro differentiation assays confirmed that the 4-1BBL on progenitors binds 4-1BB to inhibit myeloid and DC lineage differentiation.\",\n      \"method\": \"4-1BB-/- and 4-1BBL-/- mice; bone marrow chimeras; flow cytometry; in vitro differentiation assays\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO models replicated by bone marrow chimeras and in vitro assays, published in high-impact journal\",\n      \"pmids\": [\"18604213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"4-1BBL costimulation leads to TNFR-associated factor 1 (TRAF1)-dependent down-modulation of the pro-apoptotic molecule Bim in activated CD8 T cells. Reducing TRAF1 levels using siRNA resulted in increased Bim levels in 4-1BBL-stimulated T cells, demonstrating TRAF1 is required downstream of 4-1BBL signaling to suppress Bim and thereby increase T cell expansion.\",\n      \"method\": \"siRNA knockdown of TRAF1; intracellular Bim protein measurement; antigen-specific CD8 T cell expansion assays; flow cytometry\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA-mediated loss-of-function with specific molecular readout; single lab\",\n      \"pmids\": [\"18056369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Reverse signaling of 4-1BBL into monocytes (triggered by anti-4-1BBL antibody) induces their differentiation into potent dendritic cells. This process involves nuclear translocation of NF-κB and requires autocrine signaling from GM-CSF, M-CSF, and Flt3 ligand, as neutralization of these factors inhibited proliferation. The resulting DCs exhibit a Th1-inducing phenotype with elevated IL-12 and IFN-γ and reduced IL-10.\",\n      \"method\": \"Anti-4-1BBL mAb stimulation; NF-κB nuclear translocation assay; neutralizing antibodies against GM-CSF, M-CSF, and Flt3L; cytokine ELISA; flow cytometry\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional readouts and mechanistic neutralization experiments; single lab\",\n      \"pmids\": [\"19684160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"4-1BBL signaling in macrophages is dependent on glycolysis for early TLR-induced 4-1BBL expression, and the sustained late-phase 4-1BBL-mediated inflammatory response depends on glycolysis and fatty acid synthesis. Genetic ablation or antibody blockade of 4-1BBL signaling alleviated imiquimod-induced psoriasis and regulated macrophage polarization in vitro. The psoriasis-promoting effect of 4-1BBL was independent of its receptor 4-1BB (4-1BB deficiency augmented psoriasis severity through different mechanisms).\",\n      \"method\": \"4-1BBL-/- and 4-1BB-/- mice; metabolic inhibitors (2-DG, cerulenin); anti-4-1BBL antibody; 4-1BB-Fc decoy; imiquimod psoriasis model; cytokine measurement\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO and pharmacologic inhibition with specific metabolic and phenotypic readouts; single lab\",\n      \"pmids\": [\"32041783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"4-1BBL signaling promotes macrophage/monocyte proliferation by reprogramming glucose metabolism via AKT-mTOR signaling. 4-1BBL stimulation increased glucose uptake, GLUT1 expression, glycolytic enzyme levels, lactate production, and transcription of pentose phosphate pathway and lipogenesis genes. 2-deoxyglucose (glycolytic inhibitor) completely abolished 4-1BBL-induced macrophage proliferation.\",\n      \"method\": \"4-1BBL stimulation on macrophages; glucose uptake assay; Western blot; qRT-PCR; metabolic inhibitor (2-DG); AKT-mTOR pathway analysis\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal metabolic readouts with pharmacologic inhibition; single lab\",\n      \"pmids\": [\"25691217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"4-1BB/4-1BBL interaction promotes bidirectional inflammatory signaling in adipocytes and macrophages. 4-1BB is expressed on adipocytes and upregulated by obesity-related factors, which also enhance 4-1BBL expression on macrophages. 4-1BB and/or 4-1BBL agonists activated MAPK/IκBα and MAPK/Akt signaling in adipocytes and macrophages respectively, and enhanced inflammatory cytokine release (MCP-1, TNF-α, IL-6). Disruption of 4-1BB/4-1BBL interaction in contact co-culture decreased inflammatory cytokine release.\",\n      \"method\": \"Co-culture of adipocytes and macrophages; 4-1BB/4-1BBL agonists; signaling pathway (MAPK, Akt, IκBα) analysis; cytokine ELISA; blocking antibodies\",\n      \"journal\": \"Mediators of inflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based co-culture with signaling pathway analysis and blocking experiments; single lab\",\n      \"pmids\": [\"23316108\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"4-1BBL-/- mice exhibit a weaker CTL response to influenza virus compared to wild-type, while the CTL response to LCMV is normal. 4-1BBL-/-CD28-/- mice show a delay in skin allograft rejection and respond poorly to influenza. CD28-/- T cells show substantially inhibited allogeneic CTL responses to 4-1BBL-expressing APC (blocked by soluble 4-1BB receptor). TCR-transgenic CD28-/- T cells are responsive to 4-1BBL co-stimulation when a suboptimal agonist peptide is used but not with the wild-type peptide, placing 4-1BBL as a co-stimulator that augments suboptimal CTL responses.\",\n      \"method\": \"4-1BBL-/- and 4-1BBL-/-CD28-/- mice; viral infection models (influenza, LCMV); skin allograft rejection; soluble 4-1BB receptor blocking; CTL assays; TCR-transgenic CD28-/- T cells\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic KO models with multiple immune challenge readouts; independently informative epistasis\",\n      \"pmids\": [\"10528184\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Leukemic extracellular vesicles (EVs) shuttle 4-1BBL/CD137L on their surface to promote suppressive effector regulatory T cells (Tregs). 4-1BBL on leukemic EVs promoted suppressive activity and effector phenotype of Tregs by regulating expression of CD30 and TNFR2. Leukemic EV secretion is Rab27a-dependent.\",\n      \"method\": \"Leukemic EV isolation; flow cytometry; Rab27a-deficient mouse model; Treg functional assays; transcriptomic profiling\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic (Rab27a KO) and functional EV experiments; single lab\",\n      \"pmids\": [\"35130345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A homozygous missense mutation (p.V140G) in TNFSF9 (CD137L/4-1BBL) causes a loss-of-function with absent surface expression of CD137L on patient monocytes, dendritic cells, and EBV-infected B cells. Patient EBV-infected B cells failed to trigger expansion of EBV-specific T cells. T cell expansion was recovered when CD137L expression was restored on patient B cells, demonstrating that CD137L is required for CD137-mediated co-stimulation supporting EBV-specific T cell responses.\",\n      \"method\": \"Patient genetics (homozygous TNFSF9 missense mutation); ectopic expression of wild-type vs. mutant CD137L in HEK and P815 cells; flow cytometry; EBV-specific T cell expansion assays; rescue by CD137L restoration\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — natural human loss-of-function mutation with rescue experiment; direct causal link between CD137L and EBV-specific T cell expansion\",\n      \"pmids\": [\"35657354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"m4-1BBL binding to m4-1BB blocks laminin (LN) binding, whereas m4-1BB binding to LN does not block m4-1BBL binding. Truncation studies showed regions downstream of the LN-homologous domain participate in LN binding, and the intact protein is required for m4-1BBL binding. Human 4-1BB does not bind ECM proteins, only h4-1BBL, indicating this ECM-binding property is not conserved across species.\",\n      \"method\": \"Binding competition assays; truncated protein fragments; anti-4-1BB monoclonal antibody blocking panel; murine/human chimeras\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple binding competition and domain-mapping experiments; single lab\",\n      \"pmids\": [\"9045669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The scFv36-4-1BBL fusion protein (scFv against FAP fused to 4-1BBL extracellular domain) forms a homotrimeric molecule that binds FAP and 4-1BB simultaneously. T cell costimulation (measured by IFN-γ release) was concentration-dependent, ligand-specific, and substantially constrained to FAP-expressing target cells, demonstrating that targeted presentation of 4-1BBL is required for its co-stimulatory activity.\",\n      \"method\": \"Recombinant fusion protein generation; binding assays to FAP and 4-1BB; co-culture T cell costimulation assay; IFN-γ ELISA\",\n      \"journal\": \"Journal of immunotherapy (Hagerstown, Md. : 1997)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — functional in vitro assays confirming that 4-1BBL trimeric presentation is required for activity; single lab\",\n      \"pmids\": [\"18779748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Tumor cell-derived soluble CD137 (sCD137), produced under hypoxic conditions via alternative splicing lacking the transmembrane domain, binds CD137L (4-1BBL) on APCs and prevents interaction of CD137L with transmembrane CD137 on T cells, thereby blocking T cell co-stimulation. shRNA silencing of CD137 in tumor cells rendered tumors more immunogenic in immunocompetent mice but not in immunodeficient or CD8+ T cell-depleted mice.\",\n      \"method\": \"Hypoxia exposure of tumor cell lines; RT-PCR for splice variants; ELISA for sCD137; T cell co-culture with CD137L transfectants; shRNA knockdown; in vivo tumor immunogenicity assays\",\n      \"journal\": \"Oncoimmunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic co-culture blocking assay with in vivo genetic validation; single lab\",\n      \"pmids\": [\"26942078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Anti-4-1BBL monoclonal antibody (1F1) triggers reverse signaling through 4-1BBL on monocytes, inducing monocyte proliferation from peripheral blood. The same antibody inhibited T lymphocyte proliferation costimulated by soluble 4-1BBL and anti-CD3.\",\n      \"method\": \"Anti-4-1BBL mAb generation; flow cytometry; Western blotting; T cell proliferation inhibition assay; monocyte proliferation assay\",\n      \"journal\": \"Hybridoma and hybridomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single antibody-based activation experiment; single lab; no downstream signaling identified\",\n      \"pmids\": [\"14678652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CD137L-mediated reverse signaling inhibits RANKL-induced osteoclast formation in a dose-dependent manner. Cross-linking of CD137L with anti-CD137L mAb inhibited M-CSF/RANKL-evoked formation of multi-nucleated osteoclasts from bone marrow cells.\",\n      \"method\": \"Anti-CD137L mAb crosslinking; osteoclastogenesis assay from murine bone marrow and RAW264.7 cells; RANKL/M-CSF stimulation\",\n      \"journal\": \"Immunobiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single antibody-based activation assay; no downstream signaling identified; single lab\",\n      \"pmids\": [\"19167994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"miR-484 directly represses CD137L (TNFSF9) expression in MSI colorectal cancer cells. Loss of miR-484 via CpG island methylation leads to increased CD137L expression, which promotes IL-8 production by MSI CRC cells.\",\n      \"method\": \"miRNA microarray; qRT-PCR; CpG methylation analysis; miR-484 overexpression/inhibition; CD137L expression measurement; IL-8 ELISA\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional link between miR-484, CD137L, and IL-8 in matched in vitro and in vivo experiments; single lab\",\n      \"pmids\": [\"25727216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CD137-CD137L signaling promotes vascular smooth muscle cell (VSMC) phenotype transformation from contractile to synthetic via NFATc1 activation. Recombinant CD137L upregulated NFATc1 expression; contractile phenotype markers (SM-MHC, α-SMA) decreased while synthetic marker (vimentin) and cell migration increased. These effects were blocked by anti-CD137 antibody or NFATc1 siRNA, and NFATc1 overexpression alone caused phenotype transformation.\",\n      \"method\": \"Recombinant CD137L stimulation; NFATc1 siRNA and lentiviral overexpression; Western blot; immunofluorescence; Transwell migration assay; in vivo neointima model\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA and overexpression with in vitro and in vivo validation; single lab\",\n      \"pmids\": [\"28770466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"4-1BBL expressed on Batf3-lineage dendritic cells within the tumor microenvironment is a major positive co-stimulatory signal for CD8+ T cell reinvigoration and tumor regression in response to PD-1/PD-L1 blockade. Blocking 4-1BBL or depleting Batf3+ DCs abrogated the efficacy of anti-PD-1 therapy.\",\n      \"method\": \"Gene-targeted mice (Batf3-/-); anti-4-1BBL blocking antibodies; flow cytometry; spatial transcriptomics on human tumor samples; tumor regression readout\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and antibody-blocking models with spatial validation in human tumors; single lab\",\n      \"pmids\": [\"38656869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Macrophage STING signaling activates NLRP3-mediated IL-18 and IL-1β production, which promotes 4-1BBL expression on macrophages and 4-1BB expression on NK cells respectively, enabling 4-1BBL/4-1BB co-stimulation that enhances NK cell antitumor function against colorectal cancer liver metastasis.\",\n      \"method\": \"Global and myeloid-specific STING-/- mice; myeloid NLRP3-/- mice; NK cell depletion; bone marrow-derived macrophage/NK co-culture; flow cytometry; intrasplenic CRC mouse model\",\n      \"journal\": \"Journal for immunotherapy of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple genetic KO models with epistasis analysis; single lab\",\n      \"pmids\": [\"36927529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Galectin-3 (Gal-3) binds to both soluble and membrane-bound 4-1BB without blocking co-binding of 4-1BBL. Gal-3 forms large soluble 4-1BB/Gal-3 complexes (>100 nm) in plasma that attach to membrane 4-1BB on T cells, resulting in a ~4-fold decrease in TNFα production by 4-1BB+Gal-3+ T cells after 4-1BBL exposure, demonstrating Gal-3 suppresses 4-1BBL bioactivity by receptor clustering rather than direct competition.\",\n      \"method\": \"Co-binding assays; particle size analysis (plasma complexes); flow cytometry; TNFα production assay; 4-1BB-transfected HEK293 cells\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal binding and functional assays; single lab\",\n      \"pmids\": [\"35812455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hypoxia-induced lactic acid accumulation in glioma cells is absorbed by macrophages via MCT-1, leading to H3K18 lactylation (H3K18La) that epigenetically upregulates TNFSF9 expression. Elevated macrophage TNFSF9 then promotes M2 macrophage polarization and facilitates glioma progression. ChIP-seq identified H3K18La enrichment at the TNFSF9 locus. Silencing MCT-1 or the glycolysis inhibitor reversed TNFSF9 upregulation and M2 polarization.\",\n      \"method\": \"ChIP-seq for H3K18La; MCT-1 siRNA knockdown; glycolysis inhibitor; TNFSF9 knockdown; in vitro and in vivo glioma models\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-seq plus genetic and pharmacologic perturbations in vitro and in vivo; single lab\",\n      \"pmids\": [\"39010835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CD137L released by macrophages (stimulated by VEGF-C) binds to CD137 on lymphatic endothelial cells (LECs), activating PI3K/AKT/mTOR signaling that promotes autophagy (LC3-I to LC3-II conversion, Atg5, Atg7, Atg12 upregulation) and thereby enhances LEC proliferation, migration, and tube formation. Knockdown of Atg5 or Atg7 blocked CD137L-induced autophagy and lymphangiogenesis.\",\n      \"method\": \"Recombinant CD137L treatment of LECs; CD137 siRNA knockdown; Western blot (LC3, Atg proteins); PI3K/AKT/mTOR pathway analysis; Atg5/Atg7 siRNA; LEC proliferation/migration/tube formation assays; UUO mouse model\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple siRNA knockdowns with signaling pathway and functional readouts; single lab\",\n      \"pmids\": [\"35173546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SA-4-1BBL (oligomeric 4-1BBL) costimulation inhibits TGF-β- and antigen-driven conversion of naïve CD4+FoxP3- T cells into induced Tregs via stimulation of IFN-γ production by CD4+FoxP3- T cells. SA-4-1BBL also blocked conversion of CD4+ T cells into Tregs by EG.7 tumors in vivo.\",\n      \"method\": \"IFN-γ neutralization; in vitro iTreg conversion assay; in vivo tumor model with SA-4-1BBL treatment; FoxP3 expression analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic IFN-γ neutralization experiment with in vitro and in vivo validation; single lab\",\n      \"pmids\": [\"22870329\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TNFSF9 (4-1BBL/CD137L) is a trimeric TNF superfamily ligand that binds its cognate receptor 4-1BB (CD137) at the inter-protomer crevice via a distinct mechanism; crosslinking of trimeric 4-1BBL is required for co-stimulatory activity, and human 4-1BB can form CRD4 disulfide-linked dimers that amplify signaling through receptor network formation. Beyond forward 4-1BB signaling on T, NK, and myeloid cells—which promotes T cell survival via TRAF1-dependent Bim downregulation, suppresses Treg conversion via IFN-γ, and inhibits myelopoiesis—4-1BBL also transduces receptor-independent reverse signals into the cells that express it: in macrophages, it interacts with TLR4 (recruiting TIRAP/IRAK2/TRAF6/TAK1) to sustain late-phase CREB/C-EBP-dependent TNF production and regulates macrophage polarization and metabolic reprogramming via AKT-mTOR; in epithelial cells, CD137-driven CD137L reverse signaling induces CXCL1/CXCL2 secretion to recruit neutrophils during ischemia-reperfusion injury; and in monocytes, CD137L reverse signaling drives NF-κB-dependent differentiation into inflammatory dendritic cells. Structural studies confirm the canonical bell-shaped trimeric assembly of 4-1BBL in complex with 4-1BB, with important species differences between mouse (covalent dimer, GH-loop–mediated binding) and human (non-covalent trimer, distinct binding geometry) molecules, and galectin-9 or galectin-3 can modulate 4-1BB receptor clustering and signaling amplitude.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TNFSF9 (4-1BBL/CD137L) is a trimeric TNF-superfamily ligand that serves as a bidirectional immune co-stimulator, transmitting forward signals through its receptor 4-1BB (CD137) and receptor-independent reverse signals into the cells that express it [#0, #5]. Structurally, human 4-1BBL assembles as a canonical bell-shaped trimer and engages 4-1BB predominantly at one protomer via the inter-protomer crevice using a non-canonical mechanism lacking the typical DE-loop tyrosine contact; human 4-1BB additionally forms CRD4 disulfide-linked dimers that crosslink complexes into a 2D network to amplify signaling [#0, #1]. Mouse 4-1BBL diverges as a covalent disulfide-linked dimer that binds via the GH loop, a species difference proposed to be compensated by galectin-9-mediated receptor aggregation [#2, #3]. Soluble trimeric 4-1BBL alone is insufficient for co-stimulation; crosslinking of two trimers or targeted surface presentation is the minimal requirement for co-stimulatory activity [#4, #18]. Through forward signaling, 4-1BBL augments suboptimal CTL responses [#14], drives TRAF1-dependent downregulation of pro-apoptotic Bim to promote CD8 T cell expansion [#9], suppresses TGF-\\u03b2-driven Treg conversion via IFN-\\u03b3 [#29], and restrains myelopoiesis and dendritic cell differentiation [#8]. In its reverse-signaling capacity, surface 4-1BBL on macrophages forms a complex with TLR4 that recruits TIRAP, IRAK2 and the TRAF6/TAK1/TAB1 module to sustain late-phase CREB/C-EBP-dependent TNF production independent of 4-1BB, MyD88 and TRIF [#5, #6], and reprograms macrophage glucose metabolism through AKT-mTOR to support proliferation and inflammation [#11, #12]. Reverse signaling also induces CXCL1/CXCL2-driven neutrophil recruitment in epithelial cells during ischemia-reperfusion injury [#7] and NF-\\u03baB-dependent monocyte differentiation into inflammatory dendritic cells [#10]. A homozygous TNFSF9 missense mutation (p.V140G) abolishing surface CD137L causes loss of 4-1BB-mediated co-stimulation and failure of EBV-specific T cell expansion, with rescue upon restoring CD137L [#16].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established that 4-1BBL/4-1BB binding involves species-specific properties, with murine 4-1BB binding ECM laminin in a manner mutually exclusive with ligand, a feature not conserved in human.\",\n      \"evidence\": \"Binding competition and domain-mapping with truncated fragments and murine/human chimeras\",\n      \"pmids\": [\"9045669\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural basis for the species difference resolved at this stage\", \"Functional consequence of laminin binding in vivo not established\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined 4-1BBL as a co-stimulator that augments suboptimal CTL responses, separable from CD28, by showing genetic deficiency impairs antiviral and allograft responses.\",\n      \"evidence\": \"4-1BBL-/- and 4-1BBL-/-CD28-/- mice across influenza, LCMV, and allograft models with soluble receptor blocking\",\n      \"pmids\": [\"10528184\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling intermediates not identified\", \"Antigen-strength dependence mechanism unexplained\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Resolved the oligomeric requirement for co-stimulation, showing soluble trimeric ligand is insufficient and crosslinking of two trimers is the minimal activating step.\",\n      \"evidence\": \"Recombinant 4-1BBL, ultracentrifugation/gel filtration, SPR, C51 mutagenesis, and T cell proliferation assays\",\n      \"pmids\": [\"16204238\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological crosslinking mechanism on cell surfaces not defined\", \"Role of Cys-51 disulfide in vivo unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified a receptor-independent reverse-signaling function: surface 4-1BBL on macrophages associates with TLR4 to sustain late-phase TNF production via CREB/C-EBP, independent of MyD88/TRIF.\",\n      \"evidence\": \"Reciprocal Co-IP, 4-1BBL-deficient macrophages, and NF-\\u03baB/CREB/C-EBP reporter and cytokine assays\",\n      \"pmids\": [\"17496895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adaptors bridging TLR4-4-1BBL not yet identified\", \"How early signaling triggers ligand translocation unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined a forward signaling effector: 4-1BBL co-stimulation downregulates pro-apoptotic Bim via TRAF1 to promote CD8 T cell survival.\",\n      \"evidence\": \"TRAF1 siRNA knockdown with intracellular Bim measurement and antigen-specific CD8 expansion assays\",\n      \"pmids\": [\"18056369\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab siRNA loss-of-function\", \"Link between TRAF1 and Bim regulation mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed 4-1BBL forward signaling restrains myelopoiesis and DC differentiation at the progenitor level.\",\n      \"evidence\": \"4-1BB-/- and 4-1BBL-/- mice, bone marrow chimeras, and in vitro differentiation assays\",\n      \"pmids\": [\"18604213\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Intracellular signaling controlling progenitor inhibition not defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extended reverse signaling to monocytes, showing 4-1BBL engagement drives NF-\\u03baB-dependent differentiation into Th1-inducing dendritic cells.\",\n      \"evidence\": \"Anti-4-1BBL mAb stimulation, NF-\\u03baB nuclear translocation, and cytokine neutralization (GM-CSF/M-CSF/Flt3L)\",\n      \"pmids\": [\"19684160\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Antibody-driven rather than physiological ligand engagement\", \"Proximal signaling components linking ligand to NF-\\u03baB unidentified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated reverse signaling drives tissue pathology: CD137 on NK cells engages epithelial CD137L to induce CXCL1/CXCL2 and neutrophil recruitment in kidney ischemia-reperfusion injury.\",\n      \"evidence\": \"CD137-/- and CD137L-/- mice in an IRI model with chemokine measurement and neutrophil depletion\",\n      \"pmids\": [\"22160719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Intracellular reverse-signaling cascade in epithelial cells not mapped\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified the molecular intermediates of macrophage reverse signaling, placing TIRAP and IRAK2 between the TLR4-4-1BBL complex and TRAF6/TAK1-driven sustained TNF.\",\n      \"evidence\": \"Co-IP, TIRAP-/- and IRAK2-/- mice, dominant-negative constructs, and an LPS sepsis model\",\n      \"pmids\": [\"24084649\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the TLR4-4-1BBL interaction unknown\", \"How 4-1BBL recruits TIRAP/IRAK2 mechanistically unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed 4-1BBL forward co-stimulation blocks induced Treg conversion through IFN-\\u03b3.\",\n      \"evidence\": \"SA-4-1BBL oligomer, IFN-\\u03b3 neutralization, in vitro iTreg conversion, and an in vivo tumor model\",\n      \"pmids\": [\"22870329\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab; uses engineered oligomeric ligand\", \"Direct vs indirect IFN-\\u03b3 contribution not fully separated\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extended bidirectional signaling to metabolic inflammation, with 4-1BB/4-1BBL contact between adipocytes and macrophages activating MAPK/Akt/I\\u03baB\\u03b1 and inflammatory cytokine release.\",\n      \"evidence\": \"Adipocyte-macrophage co-culture, agonists, signaling analysis, and blocking antibodies\",\n      \"pmids\": [\"23316108\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Forward vs reverse signaling contributions not disentangled\", \"Single-lab co-culture system\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the metabolic basis of reverse signaling, showing 4-1BBL reprograms glucose metabolism via AKT-mTOR to drive macrophage proliferation.\",\n      \"evidence\": \"4-1BBL stimulation, glucose uptake assays, GLUT1/glycolytic enzyme analysis, and 2-DG inhibition\",\n      \"pmids\": [\"25691217\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor-independence not formally controlled in this study\", \"Single-lab metabolic readouts\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified a soluble decoy mechanism, where hypoxia-induced soluble CD137 binds CD137L on APCs and blocks T cell co-stimulation, promoting tumor immune escape.\",\n      \"evidence\": \"Hypoxia, splice-variant RT-PCR, ELISA, T cell co-culture blocking, shRNA, and in vivo tumor immunogenicity\",\n      \"pmids\": [\"26942078\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab; physiological abundance of sCD137 in human tumors not quantified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected TNFSF9 expression to epigenetic/post-transcriptional control, with miR-484 loss via CpG methylation derepressing CD137L to promote IL-8 in MSI colorectal cancer.\",\n      \"evidence\": \"miRNA microarray, methylation analysis, miR-484 gain/loss, and IL-8 measurement\",\n      \"pmids\": [\"25727216\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct miR-484-TNFSF9 binding interaction confirmation limited to single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed CD137-CD137L signaling drives vascular smooth muscle phenotype switching through NFATc1 activation.\",\n      \"evidence\": \"Recombinant CD137L, NFATc1 siRNA/overexpression, migration assays, and an in vivo neointima model\",\n      \"pmids\": [\"28770466\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Forward vs reverse signaling directionality not resolved\", \"Single-lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Provided structural detail of the murine receptor, revealing distinct CRD organization and CRD4 N-glycans that mediate galectin-9 binding, supporting a model where galectin-9 aids aggregation of the dimeric mouse system.\",\n      \"evidence\": \"X-ray crystallography of m4-1BB, SPR kinetics, and glycosylation mapping\",\n      \"pmids\": [\"29242193\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional role of galectin-9 aggregation in signaling not directly tested in vivo\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Resolved the long-disputed ligand architecture, establishing the human 4-1BBL bell-shaped trimer and a non-canonical inter-protomer binding mode, and defining how receptor CRD4 disulfide dimers amplify signaling.\",\n      \"evidence\": \"Multiple independent crystal structures of complex, free ligand, and antibody-bound receptor, with mutagenesis and cell-based agonist assays\",\n      \"pmids\": [\"30410017\", \"29720398\", \"29720399\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamics of 2D network formation on living cell surfaces not directly visualized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Clarified the species divergence in ligand assembly, defining mouse 4-1BBL as a covalent dimer with GH-loop-mediated receptor selectivity.\",\n      \"evidence\": \"Crystal structures of free and complexed m4-1BBL with structure-guided interface mutagenesis\",\n      \"pmids\": [\"30545939\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the dimeric mouse geometry achieves productive clustering not fully resolved without galectin contribution\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided definitive human causal genetics, showing a homozygous TNFSF9 loss-of-function mutation abolishes CD137L surface expression and EBV-specific T cell expansion, rescued by CD137L restoration.\",\n      \"evidence\": \"Patient genetics, ectopic wild-type vs mutant expression, and rescue of EBV-specific T cell expansion\",\n      \"pmids\": [\"35657354\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full clinical spectrum of TNFSF9 deficiency beyond EBV immunity not delineated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified galectin-3 as a modulator that suppresses 4-1BBL bioactivity by clustering receptor into large complexes rather than competing for binding.\",\n      \"evidence\": \"Co-binding assays, plasma particle sizing, flow cytometry, and TNF\\u03b1 production on 4-1BB-transfected cells\",\n      \"pmids\": [\"35812455\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of galectin-3 modulation not established\", \"Single-lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed leukemic extracellular vesicles can deliver surface 4-1BBL to promote suppressive effector Tregs, expanding the modes of ligand presentation.\",\n      \"evidence\": \"Leukemic EV isolation, Rab27a-deficient mice, Treg functional assays, and transcriptomics\",\n      \"pmids\": [\"35130345\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether vesicular 4-1BBL signals forward, reverse, or both not separated\", \"Single-lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended reverse-signaling-like activity to lymphangiogenesis, with macrophage-derived CD137L activating CD137 on lymphatic endothelial cells to drive PI3K/AKT/mTOR-dependent autophagy.\",\n      \"evidence\": \"Recombinant CD137L, CD137 and Atg5/Atg7 siRNA, pathway analysis, functional LEC assays, and a UUO model\",\n      \"pmids\": [\"35173546\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab; receptor-side signaling rather than ligand reverse signaling\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed 4-1BBL within an innate-to-NK co-stimulatory axis, where macrophage STING-NLRP3 signaling induces 4-1BBL to enhance NK antitumor function.\",\n      \"evidence\": \"STING-/- and NLRP3-/- mice, NK depletion, macrophage/NK co-culture, and a CRC liver metastasis model\",\n      \"pmids\": [\"36927529\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab; direct contribution of 4-1BBL versus IL-18/IL-1\\u03b2 partly inferred\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined 4-1BBL on Batf3-lineage dendritic cells as a major co-stimulatory signal required for CD8 T cell reinvigoration during PD-1/PD-L1 blockade.\",\n      \"evidence\": \"Batf3-/- mice, anti-4-1BBL blocking, flow cytometry, and spatial transcriptomics on human tumors\",\n      \"pmids\": [\"38656869\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab; molecular determinants of DC-restricted ligand activity not detailed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked tumor metabolism to TNFSF9 transcription, showing glioma-derived lactate drives macrophage H3K18 lactylation that upregulates TNFSF9 and promotes M2 polarization.\",\n      \"evidence\": \"ChIP-seq for H3K18La, MCT-1 and TNFSF9 knockdown, glycolysis inhibition, and in vivo glioma models\",\n      \"pmids\": [\"39010835\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab; whether the M2 effect requires 4-1BBL signaling versus correlated expression not fully separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the same trimeric ligand selects between forward co-stimulation and distinct reverse-signaling cascades in different cell types, and the structural/adaptor basis for assembling the reverse-signaling TLR4-4-1BBL-TIRAP-IRAK2 platform, remain unresolved.\",\n      \"evidence\": \"No timeline discovery resolves the molecular switch governing forward versus reverse signaling or the structure of the reverse-signaling complex\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of the 4-1BBL reverse-signaling complex with TLR4/TIRAP/IRAK2\", \"Cytoplasmic determinants of 4-1BBL reverse signaling not mapped\", \"Mechanism partitioning forward versus reverse signaling per cell type unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 4, 14, 18]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [5, 6, 7, 10]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 6, 4]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [15, 19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5, 8, 14, 24]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 9, 12, 28]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [11, 12, 27]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TNFRSF9\", \"TLR4\", \"TIRAP\", \"IRAK2\", \"TRAF1\", \"LGALS9\", \"LGALS3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}