{"gene":"NOD2","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":2001,"finding":"NOD2 frameshift mutation (3020insC) encodes a truncated protein deficient in NF-κB activation in response to bacterial lipopolysaccharides; wild-type NOD2 activates NF-κB in response to LPS, establishing NOD2 as an innate immune sensor upstream of NF-κB.","method":"Functional reporter assay (NF-κB activation) in cells expressing wild-type vs. mutant NOD2; genetic association analysis (TDT and case-control)","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct functional assay with loss-of-function mutant, widely replicated finding, foundational mechanistic paper","pmids":["11385577"],"is_preprint":false},{"year":2007,"finding":"NOD2 pathway activation by MDP or M. tuberculosis infection involves stable K63-linked polyubiquitination of RIP2 (RIPK2); this requires the E2-conjugating enzyme Ubc13, E3 ligase TRAF6, and kinase TAK1. RIP2 polyubiquitination is also required for IKKγ ubiquitination and downstream NF-κB activation.","method":"In vitro ubiquitination assays, co-immunoprecipitation, dominant-negative and knockdown approaches in macrophages infected with M. tuberculosis or treated with MDP","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Co-IP, biochemical ubiquitination assays, genetic knockouts), replicated mechanistic pathway dissection","pmids":["17947236"],"is_preprint":false},{"year":2004,"finding":"TAK1 (MAP3K7) physically interacts with NOD2 and is required for NOD2-mediated NF-κB activation in response to MDP. Conversely, NOD2 inhibits TAK1-induced NF-κB activation through its LRR domain, revealing reciprocal cross-talk. The 3020insC LRR mutation reduces this inhibitory activity.","method":"Co-immunoprecipitation, dominant-negative TAK1 overexpression, reporter gene assays (NF-κB luciferase) in RICK-deficient embryonic fibroblasts and NOD2-expressing cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and functional assays with mutants in single lab, two orthogonal methods","pmids":["15075345"],"is_preprint":false},{"year":2008,"finding":"Beta-PIX and Rac1 GTPase interact with NOD2 upon MDP stimulation and mediate membrane recruitment of NOD2 and its negative regulation. Knockdown of beta-PIX or Rac1 increases NOD2-mediated NF-κB activation and IL-8 secretion, and abrogates NOD2 interaction with its negative regulator Erbin.","method":"Co-immunoprecipitation, RNA interference knockdown, Rac1 inhibitor treatment, IL-8 secretion and NF-κB activation assays in THP-1 cells and primary human monocytes","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus functional KD in primary cells, single lab","pmids":["18684957"],"is_preprint":false},{"year":2010,"finding":"ATG16L1 and NOD2 form part of an autophagy-dependent antibacterial pathway. MDP stimulation activates autophagy and increases intracellular killing of Salmonella in an ATG16L1- and NOD2-dependent manner. CD-associated NOD2 variants impair this MDP-mediated autophagy and bacterial killing response.","method":"Immunoblot, confocal microscopy, flow cytometry, reporter gene assay, gentamicin protection assay; RNAi knockdown of NOD2 and ATG16L1; primary macrophages and dendritic cells from genotyped donors","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including functional bacterial killing assay, primary cell validation, disease variant functional comparison","pmids":["20637199"],"is_preprint":false},{"year":2012,"finding":"TRIM27 acts as an E3 ubiquitin ligase that negatively regulates NOD2. TRIM27 physically interacts with NOD2 via the nucleotide-binding domain; NOD2 activation enhances this interaction. TRIM27-dependent K48-linked ubiquitination of NOD2 leads to proteasomal degradation of NOD2 and attenuation of NOD2-mediated pro-inflammatory signaling.","method":"Co-immunoprecipitation, ubiquitination assays, proteasome inhibitor treatment, reporter gene assay; overexpression and knockdown in HeLa cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assay, and functional reporter; single lab, multiple orthogonal methods","pmids":["22829933"],"is_preprint":false},{"year":2013,"finding":"Pellino3 E3 ubiquitin ligase directly binds RIP2 kinase and catalyzes its ubiquitination downstream of NOD2. Loss of Pellino3 attenuates NOD2-induced RIP2 ubiquitination, NF-κB activation, and MAPK signaling, and exacerbates experimental colitis in mice.","method":"Co-immunoprecipitation, in vitro ubiquitination assay, Pellino3 knockout mice, cytokine measurement, colitis models","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro ubiquitination assay, KO mouse model with defined phenotype, multiple orthogonal methods","pmids":["23892723"],"is_preprint":false},{"year":2013,"finding":"p62/SQSTM1 positively regulates NOD2 signaling by associating with the nucleotide-binding domain of NOD2 through TRAF6-binding or ubiquitin-associated domains, stabilizing NOD2 oligomerization and preventing NOD2 degradation, thereby enhancing NF-κB and p38 MAPK activation and IL-1β/TNF-α production.","method":"Co-immunoprecipitation, electron microscopy of NOD2-p62 complex, reporter gene assay (NF-κB), cytokine ELISA, overexpression in macrophage-like cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ultrastructural evidence, functional reporter; single lab","pmids":["23437331"],"is_preprint":false},{"year":2016,"finding":"NOD2 (and NOD1) physically associate with IRE1α/TRAF2 at the ER membrane and are required for ER-stress-induced IL-6 production and NF-κB activation. ER stress inducers trigger NOD1/2-dependent inflammation; Brucella VceC-induced ER stress triggers NOD1/2- and RIP2-dependent inflammation that is blocked by IRE1α kinase inhibition.","method":"Genetic KO/KD cells, IRE1α kinase inhibitor, bacterial infection model (Brucella), cytokine ELISA, NF-κB reporter assay in mouse and human cells","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function in multiple cell types, pharmacological inhibitors, infection model, multiple orthogonal methods","pmids":["27007849"],"is_preprint":false},{"year":2016,"finding":"Crystal structure of rabbit NOD2 in an ADP-bound inactive closed conformation reveals that subdomains in the NOD domain are closely packed via ADP-mediated and inter-domain interactions. Blau syndrome/EOS gain-of-function mutations map to NOD subdomain interfaces and likely disrupt inter-domain interactions to facilitate conformational change to the active form; CD mutations are distributed throughout the protein affecting oligomer formation and ligand binding.","method":"X-ray crystallography of ADP-bound NOD2; mutational mapping","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional mutational analysis; high-resolution structural data","pmids":["27283905"],"is_preprint":false},{"year":2018,"finding":"XIAP ubiquitinates RIP2 downstream of NOD2, and the XIAP-RIP2 interaction (via XIAP BIR2 domain) is required for NOD2-mediated NF-κB and MAPK activation and cytokine production. RIP2 kinase activity is dispensable for NOD2 signaling; rather, the RIP2 kinase domain conformation regulates XIAP-BIR2 binding. Specific lysine residues on RIP2 serve as XIAP-dependent ubiquitination sites required for pathway signaling.","method":"XIAP antagonists, RIP2 kinase inhibitors, mutagenesis of RIP2 ubiquitination sites, co-immunoprecipitation, NF-κB reporter and cytokine production assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with mutagenesis, pharmacological and genetic tools, multiple orthogonal methods in single rigorous study","pmids":["29452636"],"is_preprint":false},{"year":2018,"finding":"Parkin E3 ubiquitin ligase directly interacts with and ubiquitylates NOD2, leading to reduced NOD2 protein levels in astrocytes. Parkin-deficient astrocytes show elevated NOD2 and exaggerated ER stress, JNK activation, and cytokine release; NOD2 knockdown in parkin-deficient astrocytes suppresses these inflammatory defects and protects neighboring neurons.","method":"Co-immunoprecipitation, ubiquitination assay, siRNA knockdown of parkin and NOD2, co-culture with dopaminergic neurons, cytokine ELISA","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assay, and functional co-culture rescue experiments; single lab","pmids":["30378174"],"is_preprint":false},{"year":2022,"finding":"N-acetylglucosamine kinase (NAGK) is required for MDP (muramyl dipeptide) activation of NOD2. NAGK phosphorylates the N-acetylmuramic acid moiety of MDP at the C6 hydroxyl position, generating 6-O-phospho-MDP, which is the actual NOD2 agonist. Unmodified MDP does not constitutively activate NOD2; NAGK-deficient macrophages are completely defective in MDP sensing.","method":"Forward genetic screen, biochemical phosphorylation assay, mass spectrometry identification of 6-O-phospho-MDP, NAGK knockout macrophages, active-site mutagenesis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — forward genetic screen, in vitro biochemical assay with mutagenesis, KO validation; multiple orthogonal methods in a single rigorous study","pmids":["36002575"],"is_preprint":false},{"year":2014,"finding":"Blau syndrome gain-of-function NOD2 mutations cluster at two locations in the NACHT domain: the ATP/Mg2+-binding site and helical domain 1. These polymorphisms likely dysregulate ATP hydrolysis and NOD2 autoinhibition, respectively. Complementary mutations in NOD1 do not mirror the NOD2 hyperactivation phenotype, indicating distinct activation/regulation mechanisms for NOD1 and NOD2.","method":"Mutational analysis of NOD2 constructs in functional assays; comparative NOD1 mutagenesis","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional mutational analysis with comparative NOD1/NOD2 experiments; single lab","pmids":["25093298"],"is_preprint":false},{"year":2009,"finding":"NOD2 activation by MDP ordinarily downregulates responses to Toll-like receptor stimulation via induction of IRF4. Cells and mice lacking NOD2 mount increased TLR responses. Administration of MDP to normal mice induces IRF4 and prevents experimental colitis, placing NOD2 as a negative regulator of TLR-driven NF-κB activation through IRF4.","method":"NOD2-deficient mice, MDP stimulation assays, NOD2 transgenic mice (increased NOD2 function), IRF4 expression analysis, experimental colitis models (DSS, TNBS)","journal":"Mucosal immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO and transgenic mouse models, in vivo colitis models, IRF4 mechanistic link; multiple complementary approaches","pmids":["19079230"],"is_preprint":false},{"year":2022,"finding":"Blau syndrome NOD2 mutations in the nucleotide-binding domain reduce canonical RIPK2-mediated NF-κB activation and impair NOD2-mediated cross-regulation of TLR responses. IRF4 upregulation is defective in cells bearing Blau NOD2 mutations, identifying IRF4 as the proximal mediator of NOD2 cross-regulatory suppression of NF-κB. In vivo, mice bearing Blau mutations fail to suppress colitis or arthritis in response to MDP.","method":"Overexpression of Blau NOD2 mutants in HEK293 cells, reporter assays, experimental colitis and arthritis models, lentiviral IRF4 transduction rescue, IRF4 expression in patient-derived macrophages","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo functional assays, patient material; single lab but multiple approaches","pmids":["36189261"],"is_preprint":false},{"year":2017,"finding":"NOD2 suppresses colorectal tumorigenesis via downregulation of TLR signaling pathways. In vitro, NOD2 activation by MDP inhibits TLR-mediated NF-κB and MAPK activation, associated with induction of IRF4. Nod2-deficient mice show higher NF-κB, ERK, and STAT3 activation during colitis and colorectal tumorigenesis.","method":"Nod2-/- mouse colorectal tumorigenesis model, in vitro MDP stimulation with TLR co-stimulation, NF-κB/MAPK/STAT3 activation assays, IRF4 expression analysis","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse model with in vitro mechanistic follow-up; single lab, two complementary approaches","pmids":["28658623"],"is_preprint":false},{"year":2009,"finding":"Nod2 is required for controlling commensal bacterial load in the intestinal terminal ileum. Nod2-deficient mice harbor increased commensal bacteria and have diminished ability to prevent intestinal colonization by pathogens. Intestinal crypts from Nod2-/- mice are unable to kill bacteria effectively in vitro. Nod2 expression in the terminal ileum is dependent on the presence of commensal bacteria, establishing a feedback regulatory mechanism.","method":"Nod2 knockout mice, bacterial quantification from terminal ilea, in vitro crypt bacterial killing assay, germ-free mouse reconstitution","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse model, germ-free reconstitution, in vitro crypt killing assay; multiple orthogonal methods","pmids":["19805227"],"is_preprint":false},{"year":2022,"finding":"NOD2 in intestinal epithelial cells is necessary for LpWJL bacteria-mediated IGF-1 production and postnatal growth promotion in malnourished conventional animals. Muramyl dipeptide and mifamurtide (MDP analogs) are sufficient as NOD2 ligands to stimulate animal growth during undernutrition.","method":"Conditional and constitutive Nod2 knockout mice, MDP and mifamurtide administration, IGF-1 measurement, germ-free and conventional malnourished mouse models","journal":"Science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO localizes function to intestinal epithelial cells, pharmacological ligand validation; single study","pmids":["36821686"],"is_preprint":false},{"year":2022,"finding":"In mice, NOD2 is expressed in hypothalamic inhibitory neurons and is activated by muropeptides reaching the brain. Activation of neuronal NOD2 by bacterial peptidoglycan-derived muropeptides regulates appetite and body temperature control, primarily in females.","method":"Nod2 knockout mice, live brain imaging, peptidoglycan/muropeptide brain delivery, neuronal activity recording, food intake and body temperature measurement","journal":"Science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse model with defined neuronal phenotype, peptidoglycan delivery experiment; single study","pmids":["35420957"],"is_preprint":false},{"year":2021,"finding":"NOD2 deficiency increases retrograde transport of secretory IgA (SIgA)-pathogen complexes through intestinal M cells by upregulating Dectin-1 and Siglec-5 expression. NOD2 normally downregulates these M cell receptors to limit SIgA retrograde transport.","method":"NOD2-deficient human patients and mouse models, M cell receptor expression analysis, SIgA transport assays, receptor KD experiments","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human and mouse loss-of-function data, receptor expression and functional transport assay; single study","pmids":["33431850"],"is_preprint":false},{"year":2020,"finding":"NOD2 exerts anti-tumor effects in hepatocellular carcinoma by directly binding the AMPKα-LKB1 complex, activating AMPK signaling, and triggering autophagy-mediated apoptosis. NOD2 also enhances chemosensitivity to sorafenib, lenvatinib, and 5-FU through AMPK pathway activation.","method":"Co-immunoprecipitation of NOD2 with AMPKα-LKB1, Nod2-/- mouse HCC model, xenograft model, in vitro proliferation and invasion assays, AMPK pathway activation assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating direct binding, KO mouse model, multiple cell-based functional assays; single lab","pmids":["32144252"],"is_preprint":false},{"year":2022,"finding":"Gut microbial DL-endopeptidase increases the level of NOD2 ligand (muropeptides) in the intestinal lumen. Administration of active DL-endopeptidase, but not an active-site mutant, alleviates colitis via the NOD2 pathway. This establishes that microbially-generated NOD2 ligand availability is a mechanism linking microbiome composition to NOD2-dependent intestinal homeostasis.","method":"Metagenomic analysis, active-site DL-endopeptidase mutant control, colitis mouse models (NOD2-dependent rescue), fecal microbiota transplant","journal":"Cell host & microbe","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — active-site mutant control establishes enzymatic mechanism, NOD2 KO rescue validates pathway; single study","pmids":["36049483"],"is_preprint":false},{"year":2007,"finding":"Activation of NOD2 by its agonist MDP induces CCL5/RANTES secretion from murine macrophages through the NF-κB pathway, not through the interferon-β pathway. In vivo, intraperitoneal injection of NOD2 agonists causes rapid CCL5 secretion into the bloodstream.","method":"Murine macrophage stimulation with Nod2 agonists, CCL5 ELISA, NF-κB promoter reporter assay, IFN-β pathway analysis, in vivo peritoneal injection model","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo functional assays, pathway dissection; single lab","pmids":["17705131"],"is_preprint":false},{"year":2014,"finding":"NOD2 stimulation by MDP inhibits odontoblast differentiation of human dental pulp cells through increased MKP-1 protein expression and subsequent dephosphorylation/inactivation of MAPKs required for differentiation. NOD2 siRNA knockdown reverses MDP-mediated inhibition of differentiation.","method":"siRNA knockdown of NOD2, ALP activity assay, mineralization assay, MAPK phosphorylation analysis, MKP-1 expression analysis in human dental pulp cells","journal":"Journal of dental research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — functional siRNA KD in cell line; single lab, single study","pmids":["24820666"],"is_preprint":false},{"year":2017,"finding":"iPSC-derived macrophages with Blau syndrome NOD2 mutations show IFN-γ-dependent, ligand-independent NF-κB activation and proinflammatory cytokine production. IFN-γ acts as a priming signal by upregulating NOD2 expression, and correction of the NOD2 mutation by CRISPR-Cas9 normalizes inflammatory responses.","method":"Blau syndrome-specific iPSC derivation, CRISPR-Cas9 isogenic correction and introduction of NOD2 mutation, iPSC differentiation to macrophages, NF-κB activation assays, cytokine measurements, RNA-seq","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — isogenic CRISPR correction and mutation introduction with multiple orthogonal readouts; rigorous causal mechanistic study","pmids":["28587749"],"is_preprint":false},{"year":2014,"finding":"miR-192, miR-495, miR-512, and miR-671 directly suppress NOD2 expression by targeting its 3'UTR, thereby suppressing MDP-mediated NF-κB activation and IL-8/CXCL3 expression in colonic epithelial cells. A SNP (rs3135500) in the NOD2 3'UTR reduces miR-192 effectiveness.","method":"Luciferase reporter constructs with NOD2 3'UTR, miRNA mimic transfection, qRT-PCR, NF-κB reporter assays in HCT116 cells","journal":"Inflammatory bowel diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase 3'UTR reporter and functional miRNA overexpression assays with SNP validation; single lab","pmids":["24297055"],"is_preprint":false}],"current_model":"NOD2 is an intracellular innate immune pattern recognition receptor that senses bacterial peptidoglycan-derived muramyl dipeptide (specifically after NAGK-mediated phosphorylation to 6-O-phospho-MDP) via its LRR domain, oligomerizes via its NACHT domain in an ADP/ATP-regulated manner, and recruits RIP2/RIPK2 (through CARD-CARD interactions) to activate NF-κB and MAPK pathways via a ubiquitin-dependent cascade involving TRAF6, TAK1, Pellino3, and XIAP-mediated K63-linked ubiquitination of RIP2; negative regulation occurs through TRIM27- and Parkin-mediated K48-linked ubiquitination and proteasomal degradation of NOD2, and through IRF4 induction that suppresses concurrent TLR responses; NOD2 also intersects with ER stress signaling via IRE1α/TRAF2 and promotes autophagy via ATG16L1 to clear intracellular bacteria, while Blau syndrome gain-of-function mutations in the NACHT domain disrupt autoinhibitory inter-domain contacts causing ligand-independent NF-κB activation, and Crohn's disease loss-of-function mutations impair MDP sensing, bacterial killing, defensin expression, microbiota regulation, and IRF4-mediated cross-regulation of TLR responses."},"narrative":{"mechanistic_narrative":"NOD2 is an intracellular innate immune pattern-recognition receptor that senses bacterial peptidoglycan and converts this detection into NF-κB- and MAPK-driven inflammatory and antibacterial responses, originally established through loss-of-function frameshift mutation (3020insC) that abrogates NF-κB activation [PMID:11385577]. The proximal agonist is not muramyl dipeptide (MDP) itself but 6-O-phospho-MDP, generated when NAGK phosphorylates the N-acetylmuramic acid moiety; NAGK-deficient macrophages are completely defective in MDP sensing [PMID:36002575]. Crystallographic analysis of ADP-bound NOD2 shows a closed, autoinhibited conformation maintained by inter-domain and nucleotide-mediated contacts within the NOD/NACHT domain [PMID:27283905]. Upon activation, NOD2 signals through RIP2/RIPK2, whose K63-linked polyubiquitination by TRAF6/Ubc13 with TAK1, by the E3 ligase Pellino3, and by XIAP (via its BIR2 domain) drives downstream IKKγ ubiquitination and NF-κB/MAPK activation; RIP2 kinase activity is dispensable, serving instead to position the kinase domain for XIAP binding [PMID:17947236, PMID:23892723, PMID:29452636]. Beyond canonical inflammation, NOD2 couples MDP sensing to ATG16L1-dependent autophagy for intracellular bacterial killing, and Crohn's-associated NOD2 variants impair this response [PMID:20637199]. NOD2 also acts as a negative regulator, dampening Toll-like-receptor-driven NF-κB through induction of IRF4, a cross-regulatory function important for restraining colitis and colorectal tumorigenesis [PMID:19079230, PMID:28658623]. NOD2 protein levels are tightly controlled by E3 ligases TRIM27 and Parkin, which catalyze K48-linked ubiquitination and proteasomal degradation, while p62/SQSTM1 stabilizes NOD2 oligomers [PMID:22829933, PMID:23437331, PMID:30378174]. In vivo, NOD2 controls commensal bacterial load and crypt antibacterial killing in the terminal ileum, where its expression itself depends on the microbiota [PMID:19805227]. Gain-of-function mutations in the NACHT domain cause Blau syndrome through ligand-independent, IFN-γ-primed NF-κB activation [PMID:25093298, PMID:28587749].","teleology":[{"year":2001,"claim":"Established NOD2 as an innate immune sensor functioning upstream of NF-κB, with a disease-associated truncating mutation defining loss of function.","evidence":"NF-κB reporter assays comparing wild-type versus 3020insC mutant NOD2, plus genetic association analysis","pmids":["11385577"],"confidence":"High","gaps":["Did not identify the precise physiological ligand","Did not define the downstream adaptor/effector cascade"]},{"year":2004,"claim":"Identified TAK1 as a NOD2-interacting kinase required for MDP-induced NF-κB, revealing reciprocal cross-talk via the LRR domain.","evidence":"Co-IP, dominant-negative TAK1, and NF-κB reporter assays in RICK-deficient fibroblasts","pmids":["15075345"],"confidence":"Medium","gaps":["Mechanism of LRR-mediated inhibition not structurally resolved","Single-lab Co-IP without reciprocal genetic validation"]},{"year":2007,"claim":"Defined the ubiquitin-dependent core of NOD2 signaling, showing K63-linked polyubiquitination of RIP2 is required for IKKγ ubiquitination and NF-κB activation.","evidence":"In vitro ubiquitination assays, Co-IP, knockdown/dominant-negative in M. tuberculosis-infected and MDP-treated macrophages","pmids":["17947236"],"confidence":"High","gaps":["Did not establish whether multiple E3 ligases act redundantly","Site-specific RIP2 ubiquitination not yet mapped"]},{"year":2007,"claim":"Showed NOD2 activation produces a specific chemokine output (CCL5/RANTES) through NF-κB rather than the interferon-β pathway.","evidence":"Murine macrophage MDP stimulation, CCL5 ELISA, NF-κB reporter, and in vivo injection","pmids":["17705131"],"confidence":"Medium","gaps":["Scope of NOD2-driven chemokine repertoire not defined","Single-lab study"]},{"year":2009,"claim":"Reframed NOD2 as a negative regulator of innate immunity by showing MDP-induced IRF4 suppresses TLR-driven NF-κB and prevents experimental colitis.","evidence":"NOD2-deficient and transgenic mice, MDP stimulation, IRF4 analysis, DSS/TNBS colitis models","pmids":["19079230"],"confidence":"High","gaps":["Mechanism by which NOD2 induces IRF4 not detailed","Cell-type-specific contributions not separated"]},{"year":2009,"claim":"Established an in vivo physiological role for NOD2 in controlling commensal load and crypt antibacterial killing, with a microbiota-dependent expression feedback loop.","evidence":"Nod2 knockout mice, terminal ileum bacterial quantification, in vitro crypt killing, germ-free reconstitution","pmids":["19805227"],"confidence":"High","gaps":["Effector mechanism of crypt killing (e.g. specific antimicrobials) not resolved here","Direct link to human disease variants not tested"]},{"year":2010,"claim":"Connected NOD2 sensing to autophagy-mediated bacterial clearance via ATG16L1 and showed Crohn's variants impair this antibacterial arm.","evidence":"Gentamicin protection, confocal microscopy, RNAi of NOD2/ATG16L1, primary cells from genotyped donors","pmids":["20637199"],"confidence":"High","gaps":["Molecular link between NOD2 and ATG16L1 recruitment not fully defined","Relative contribution of autophagy versus NF-κB arm not quantified"]},{"year":2012,"claim":"Identified TRIM27 as an E3 ligase that terminates NOD2 signaling via K48-linked ubiquitination and proteasomal degradation.","evidence":"Co-IP, ubiquitination assays, proteasome inhibition, reporter assays in HeLa","pmids":["22829933"],"confidence":"Medium","gaps":["In vivo relevance not tested","Single-lab overexpression system"]},{"year":2013,"claim":"Added Pellino3 as a positive E3 ligase ubiquitinating RIP2 downstream of NOD2, with an in vivo colitis phenotype.","evidence":"Co-IP, in vitro ubiquitination, Pellino3 knockout mice, colitis models","pmids":["23892723"],"confidence":"High","gaps":["Hierarchy among RIP2 E3 ligases (TRAF6, Pellino3, XIAP) unresolved","Ubiquitin chain linkage specificity not fully detailed"]},{"year":2013,"claim":"Showed p62/SQSTM1 positively regulates NOD2 by stabilizing oligomerization and preventing degradation.","evidence":"Co-IP, electron microscopy of NOD2-p62 complex, NF-κB reporter, cytokine ELISA","pmids":["23437331"],"confidence":"Medium","gaps":["In vivo requirement not established","Single-lab study"]},{"year":2014,"claim":"Localized Blau syndrome gain-of-function mutations to the ATP/Mg2+-binding site and helical domain 1 of the NACHT domain, distinguishing NOD2 activation/regulation from NOD1.","evidence":"Mutational functional analysis of NOD2 constructs with comparative NOD1 mutagenesis","pmids":["25093298"],"confidence":"Medium","gaps":["Structural mechanism inferred not directly visualized","Single-lab functional assays"]},{"year":2014,"claim":"Demonstrated post-transcriptional control of NOD2 by multiple miRNAs targeting its 3'UTR, with a disease-associated SNP modulating miRNA efficacy.","evidence":"3'UTR luciferase reporters, miRNA mimics, NF-κB reporters in colonic epithelial cells","pmids":["24297055"],"confidence":"Medium","gaps":["Physiological/in vivo relevance not tested","Relative dominance among the four miRNAs unclear"]},{"year":2014,"claim":"Extended NOD2 signaling beyond immunity to inhibition of odontoblast differentiation via MKP-1-mediated MAPK inactivation.","evidence":"siRNA knockdown, differentiation and mineralization assays, MAPK/MKP-1 analysis in dental pulp cells","pmids":["24820666"],"confidence":"Low","gaps":["Single-lab cell-line study not independently confirmed","No in vivo validation"]},{"year":2016,"claim":"Provided the structural basis of NOD2 autoinhibition, showing an ADP-bound closed conformation whose interfaces are disrupted by Blau gain-of-function mutations.","evidence":"X-ray crystallography of ADP-bound rabbit NOD2 with mutational mapping","pmids":["27283905"],"confidence":"High","gaps":["Active oligomeric (ligand-bound) state not captured","LRR-ligand engagement not visualized in this structure"]},{"year":2016,"claim":"Linked NOD2 to ER stress signaling, showing physical association with IRE1α/TRAF2 and requirement for ER-stress- and infection-induced inflammation.","evidence":"Genetic KO/KD cells, IRE1α kinase inhibitor, Brucella infection model, cytokine and NF-κB assays","pmids":["27007849"],"confidence":"High","gaps":["Whether ER stress sensing requires peptidoglycan ligand unclear","Direct NOD2-IRE1α interaction interface not mapped"]},{"year":2017,"claim":"Demonstrated NOD2 suppresses colorectal tumorigenesis through IRF4-associated downregulation of TLR/NF-κB/MAPK/STAT3 signaling.","evidence":"Nod2-/- colorectal tumor model with in vitro MDP/TLR co-stimulation","pmids":["28658623"],"confidence":"Medium","gaps":["Causal role of IRF4 in tumor suppression not directly tested","Epithelial versus immune cell contribution unresolved"]},{"year":2017,"claim":"Established causal, mutation-specific Blau syndrome mechanism: ligand-independent NF-κB activation requiring IFN-γ priming, reversible by isogenic CRISPR correction.","evidence":"Blau patient iPSC-derived macrophages, CRISPR isogenic correction/introduction, NF-κB and cytokine assays, RNA-seq","pmids":["28587749"],"confidence":"High","gaps":["Mechanism of IFN-γ-driven NOD2 priming not fully dissected","Generalizability across Blau mutations not exhaustively tested"]},{"year":2018,"claim":"Defined XIAP as an essential RIP2 E3 ligase acting via its BIR2 domain and showed RIP2 kinase activity is dispensable, with the kinase domain conformation regulating XIAP binding.","evidence":"XIAP antagonists, RIP2 kinase inhibitors, ubiquitination-site mutagenesis, Co-IP, reporter and cytokine assays","pmids":["29452636"],"confidence":"High","gaps":["Functional hierarchy with TRAF6/Pellino3 not reconciled","Structural basis of kinase-domain/BIR2 coupling not solved"]},{"year":2018,"claim":"Showed Parkin ubiquitylates and degrades NOD2 in astrocytes, linking NOD2 dysregulation to neuroinflammation and neuronal toxicity.","evidence":"Co-IP, ubiquitination assay, parkin/NOD2 siRNA, dopaminergic neuron co-culture rescue","pmids":["30378174"],"confidence":"Medium","gaps":["In vivo neurodegeneration relevance not established","Single-lab study"]},{"year":2020,"claim":"Identified a non-immune, anti-tumor function of NOD2 in hepatocellular carcinoma through direct binding to the AMPKα-LKB1 complex and autophagy-mediated apoptosis.","evidence":"Co-IP, Nod2-/- HCC and xenograft models, AMPK pathway and proliferation/invasion assays","pmids":["32144252"],"confidence":"Medium","gaps":["Whether this is peptidoglycan-ligand dependent unclear","Single-lab mechanistic study"]},{"year":2021,"claim":"Revealed NOD2 controls intestinal M-cell receptor expression, limiting retrograde transport of SIgA-pathogen complexes by suppressing Dectin-1 and Siglec-5.","evidence":"Human NOD2-deficient patients and mouse models, M-cell receptor expression and SIgA transport assays","pmids":["33431850"],"confidence":"Medium","gaps":["Signaling pathway linking NOD2 to receptor repression undefined","Single study"]},{"year":2022,"claim":"Redefined the true NOD2 agonist by showing NAGK phosphorylates MDP to 6-O-phospho-MDP, which is required for NOD2 activation.","evidence":"Forward genetic screen, biochemical phosphorylation assay, mass spectrometry, NAGK-KO macrophages, active-site mutagenesis","pmids":["36002575"],"confidence":"High","gaps":["Structural basis of 6-O-phospho-MDP recognition by NOD2 LRR not solved","Whether all NOD2 ligands require NAGK modification unclear"]},{"year":2022,"claim":"Showed Blau NACHT mutations paradoxically impair canonical RIPK2 signaling and IRF4-mediated cross-regulation, identifying IRF4 as the proximal mediator of NOD2 suppression of TLR/NF-κB in vivo.","evidence":"Blau mutant overexpression, reporter assays, colitis/arthritis models, lentiviral IRF4 rescue, patient macrophages","pmids":["36189261"],"confidence":"Medium","gaps":["Reconciliation with gain-of-function inflammatory phenotype not fully clarified","Single-lab study"]},{"year":2022,"claim":"Demonstrated microbial DL-endopeptidase availability controls luminal NOD2 ligand levels, linking microbiome enzymatic activity to NOD2-dependent intestinal homeostasis.","evidence":"Metagenomics, active-site mutant control, NOD2-dependent colitis rescue, fecal transplant","pmids":["36049483"],"confidence":"Medium","gaps":["Identity of the specific muropeptide species not fully defined","Single study"]},{"year":2022,"claim":"Extended NOD2 function to systemic physiology, showing intestinal epithelial NOD2 mediates microbiota-driven IGF-1 production and postnatal growth during undernutrition.","evidence":"Conditional and constitutive Nod2 KO mice, MDP/mifamurtide administration, IGF-1 measurement, germ-free models","pmids":["36821686"],"confidence":"Medium","gaps":["Signaling pathway from epithelial NOD2 to IGF-1 not detailed","Single study"]},{"year":2022,"claim":"Identified a neuronal role for NOD2 in hypothalamic inhibitory neurons regulating appetite and body temperature in response to bacterial muropeptides.","evidence":"Nod2 KO mice, live brain imaging, muropeptide brain delivery, neuronal recording, food intake/temperature measurement","pmids":["35420957"],"confidence":"Medium","gaps":["Downstream neuronal signaling pathway undefined","Sex-specific mechanism not explained"]},{"year":null,"claim":"How ligand-bound NOD2 transitions from the autoinhibited ADP-bound state to an active oligomer that recruits RIP2, and how the competing positive and negative ubiquitin E3 ligases are coordinated in time and tissue, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the active, ligand-engaged NOD2 oligomer","Functional hierarchy among TRAF6, Pellino3, XIAP, TRIM27, and Parkin not integrated","Mechanism connecting NOD2 to ATG16L1, IRF4, and AMPK arms not unified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[9,13]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[0,12]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,12]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[14,16]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[9]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,14,17]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,10]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[4,21]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[8]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[5,11,10]}],"complexes":[],"partners":["RIPK2","MAP3K7","TRAF6","XIAP","TRIM27","PARK2","SQSTM1","ERN1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9HC29","full_name":"Nucleotide-binding oligomerization domain-containing protein 2","aliases":["Caspase recruitment domain-containing protein 15","Inflammatory bowel disease protein 1"],"length_aa":1040,"mass_kda":115.3,"function":"Pattern recognition receptor (PRR) that detects bacterial peptidoglycan fragments and other danger signals and plays an important role in gastrointestinal immunity (PubMed:12514169, PubMed:12527755, PubMed:12626759, PubMed:15044951, PubMed:15998797, PubMed:27283905, PubMed:27748583, PubMed:31649195). Specifically activated by muramyl dipeptide (MDP), a fragment of bacterial peptidoglycan found in every bacterial peptidoglycan type (PubMed:12514169, PubMed:12527755, PubMed:12626759, PubMed:12871942, PubMed:15044951, PubMed:15198989, PubMed:15998797, PubMed:22857257, PubMed:23322906, PubMed:27748583, PubMed:36002575). NOD2 specifically recognizes and binds 6-O-phospho-MDP, the phosphorylated form of MDP, which is generated by NAGK (PubMed:36002575). 6-O-phospho-MDP-binding triggers oligomerization that facilitates the binding and subsequent activation of the proximal adapter receptor-interacting RIPK2 (PubMed:11087742, PubMed:17355968, PubMed:21887730, PubMed:23806334, PubMed:28436939). Following recruitment, RIPK2 undergoes 'Met-1'- (linear) and 'Lys-63'-linked polyubiquitination by E3 ubiquitin-protein ligases XIAP, BIRC2, BIRC3 and the LUBAC complex, becoming a scaffolding protein for downstream effectors, triggering activation of the NF-kappa-B and MAP kinases signaling (PubMed:11087742, PubMed:12514169, PubMed:12626759, PubMed:15198989, PubMed:21887730, PubMed:23322906, PubMed:23806334, PubMed:28436939). This in turn leads to the transcriptional activation of hundreds of genes involved in immune response (PubMed:15198989). Its ability to detect bacterial MDP plays a central role in maintaining the equilibrium between intestinal microbiota and host immune responses to control inflammation (By similarity). An imbalance in this relationship results in dysbiosis, whereby pathogenic bacteria prevail on commensals, causing damage in the intestinal epithelial barrier as well as allowing bacterial invasion and inflammation (By similarity). Acts as a regulator of appetite by sensing MDP in a subset of brain neurons: microbiota-derived MDP reach the brain, where they bind and activate NOD2 in inhibitory hypothalamic neurons, decreasing neuronal activity, thereby regulating satiety and body temperature (By similarity). NOD2-dependent MDP-sensing of bacterial cell walls in the intestinal epithelial compartment contributes to sustained postnatal growth upon undernutrition (By similarity). Also plays a role in antiviral response by acting as a sensor of single-stranded RNA (ssRNA) from viruses: upon ssRNA-binding, interacts with MAVS, leading to activation of interferon regulatory factor-3/IRF3 and expression of type I interferon (PubMed:19701189). Also acts as a regulator of autophagy in dendritic cells via its interaction with ATG16L1, possibly by recruiting ATG16L1 at the site of bacterial entry (PubMed:20637199). NOD2 activation in the small intestine crypt also contributes to intestinal stem cells survival and function: acts by promoting mitophagy via its association with ATG16L1 (By similarity). In addition to its main role in innate immunity, also regulates the adaptive immune system by acting as regulator of helper T-cell and regulatory T-cells (Tregs) (By similarity). Besides recognizing pathogens, also involved in the endoplasmic reticulum stress response: acts by sensing and binding to the cytosolic metabolite sphingosine-1-phosphate generated in response to endoplasmic reticulum stress, initiating an inflammation process that leads to activation of the NF-kappa-B and MAP kinases signaling (PubMed:27007849, PubMed:33942347). May also be involved in NLRP1 activation following activation by MDP, leading to CASP1 activation and IL1B release in macrophages (PubMed:18511561) Acts as a pattern recognition receptor (PRR); able to activate NF-kappa-B Can activate NF-kappa-B in a muramyl dipeptide (MDP)-independent manner","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9HC29/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NOD2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NOD2","total_profiled":1310},"omim":[{"mim_id":"618051","title":"INNATE IMMUNITY ACTIVATOR; INAVA","url":"https://www.omim.org/entry/618051"},{"mim_id":"617321","title":"YAO SYNDROME; YAOS","url":"https://www.omim.org/entry/617321"},{"mim_id":"615929","title":"ANKYRIN REPEAT DOMAIN-CONTAINING PROTEIN 17; ANKRD17","url":"https://www.omim.org/entry/615929"},{"mim_id":"615806","title":"SOLUTE CARRIER FAMILY 15 (OLIGOPEPTIDE TRANSPORTER), MEMBER 4; SLC15A4","url":"https://www.omim.org/entry/615806"},{"mim_id":"614061","title":"OLFACTOMEDIN 4; OLFM4","url":"https://www.omim.org/entry/614061"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Golgi apparatus","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":10.0},{"tissue":"esophagus","ntpm":9.5},{"tissue":"skin 1","ntpm":12.8},{"tissue":"vagina","ntpm":10.2}],"url":"https://www.proteinatlas.org/search/NOD2"},"hgnc":{"alias_symbol":["BLAU","CD","PSORAS1","CLR16.3","NLRC2"],"prev_symbol":["IBD1","CARD15"]},"alphafold":{"accession":"Q9HC29","domains":[{"cath_id":"-","chopping":"40-206","consensus_level":"medium","plddt":82.7715,"start":40,"end":206},{"cath_id":"3.40.50.300","chopping":"218-448","consensus_level":"high","plddt":82.5604,"start":218,"end":448},{"cath_id":"-","chopping":"538-634_659-708","consensus_level":"medium","plddt":88.0688,"start":538,"end":708},{"cath_id":"3.80.10.10","chopping":"871-1040","consensus_level":"medium","plddt":96.6433,"start":871,"end":1040}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HC29","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HC29-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HC29-F1-predicted_aligned_error_v6.png","plddt_mean":84.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NOD2","jax_strain_url":"https://www.jax.org/strain/search?query=NOD2"},"sequence":{"accession":"Q9HC29","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9HC29.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9HC29/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HC29"}},"corpus_meta":[{"pmid":"11385577","id":"PMC_11385577","title":"A frameshift mutation in NOD2 associated with susceptibility to Crohn's disease.","date":"2001","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/11385577","citation_count":3800,"is_preprint":false},{"pmid":"25526305","id":"PMC_25526305","title":"NOD1 and NOD2: signaling, host defense, and inflammatory disease.","date":"2014","source":"Immunity","url":"https://pubmed.ncbi.nlm.nih.gov/25526305","citation_count":649,"is_preprint":false},{"pmid":"16493424","id":"PMC_16493424","title":"Signalling pathways and molecular interactions of NOD1 and NOD2.","date":"2006","source":"Nature reviews. 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RIP2 polyubiquitination is also required for IKKγ ubiquitination and downstream NF-κB activation.\",\n      \"method\": \"In vitro ubiquitination assays, co-immunoprecipitation, dominant-negative and knockdown approaches in macrophages infected with M. tuberculosis or treated with MDP\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Co-IP, biochemical ubiquitination assays, genetic knockouts), replicated mechanistic pathway dissection\",\n      \"pmids\": [\"17947236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"TAK1 (MAP3K7) physically interacts with NOD2 and is required for NOD2-mediated NF-κB activation in response to MDP. Conversely, NOD2 inhibits TAK1-induced NF-κB activation through its LRR domain, revealing reciprocal cross-talk. The 3020insC LRR mutation reduces this inhibitory activity.\",\n      \"method\": \"Co-immunoprecipitation, dominant-negative TAK1 overexpression, reporter gene assays (NF-κB luciferase) in RICK-deficient embryonic fibroblasts and NOD2-expressing cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and functional assays with mutants in single lab, two orthogonal methods\",\n      \"pmids\": [\"15075345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Beta-PIX and Rac1 GTPase interact with NOD2 upon MDP stimulation and mediate membrane recruitment of NOD2 and its negative regulation. Knockdown of beta-PIX or Rac1 increases NOD2-mediated NF-κB activation and IL-8 secretion, and abrogates NOD2 interaction with its negative regulator Erbin.\",\n      \"method\": \"Co-immunoprecipitation, RNA interference knockdown, Rac1 inhibitor treatment, IL-8 secretion and NF-κB activation assays in THP-1 cells and primary human monocytes\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus functional KD in primary cells, single lab\",\n      \"pmids\": [\"18684957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ATG16L1 and NOD2 form part of an autophagy-dependent antibacterial pathway. MDP stimulation activates autophagy and increases intracellular killing of Salmonella in an ATG16L1- and NOD2-dependent manner. CD-associated NOD2 variants impair this MDP-mediated autophagy and bacterial killing response.\",\n      \"method\": \"Immunoblot, confocal microscopy, flow cytometry, reporter gene assay, gentamicin protection assay; RNAi knockdown of NOD2 and ATG16L1; primary macrophages and dendritic cells from genotyped donors\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including functional bacterial killing assay, primary cell validation, disease variant functional comparison\",\n      \"pmids\": [\"20637199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TRIM27 acts as an E3 ubiquitin ligase that negatively regulates NOD2. TRIM27 physically interacts with NOD2 via the nucleotide-binding domain; NOD2 activation enhances this interaction. TRIM27-dependent K48-linked ubiquitination of NOD2 leads to proteasomal degradation of NOD2 and attenuation of NOD2-mediated pro-inflammatory signaling.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, proteasome inhibitor treatment, reporter gene assay; overexpression and knockdown in HeLa cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assay, and functional reporter; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"22829933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Pellino3 E3 ubiquitin ligase directly binds RIP2 kinase and catalyzes its ubiquitination downstream of NOD2. Loss of Pellino3 attenuates NOD2-induced RIP2 ubiquitination, NF-κB activation, and MAPK signaling, and exacerbates experimental colitis in mice.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitination assay, Pellino3 knockout mice, cytokine measurement, colitis models\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro ubiquitination assay, KO mouse model with defined phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"23892723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"p62/SQSTM1 positively regulates NOD2 signaling by associating with the nucleotide-binding domain of NOD2 through TRAF6-binding or ubiquitin-associated domains, stabilizing NOD2 oligomerization and preventing NOD2 degradation, thereby enhancing NF-κB and p38 MAPK activation and IL-1β/TNF-α production.\",\n      \"method\": \"Co-immunoprecipitation, electron microscopy of NOD2-p62 complex, reporter gene assay (NF-κB), cytokine ELISA, overexpression in macrophage-like cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ultrastructural evidence, functional reporter; single lab\",\n      \"pmids\": [\"23437331\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"NOD2 (and NOD1) physically associate with IRE1α/TRAF2 at the ER membrane and are required for ER-stress-induced IL-6 production and NF-κB activation. ER stress inducers trigger NOD1/2-dependent inflammation; Brucella VceC-induced ER stress triggers NOD1/2- and RIP2-dependent inflammation that is blocked by IRE1α kinase inhibition.\",\n      \"method\": \"Genetic KO/KD cells, IRE1α kinase inhibitor, bacterial infection model (Brucella), cytokine ELISA, NF-κB reporter assay in mouse and human cells\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function in multiple cell types, pharmacological inhibitors, infection model, multiple orthogonal methods\",\n      \"pmids\": [\"27007849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of rabbit NOD2 in an ADP-bound inactive closed conformation reveals that subdomains in the NOD domain are closely packed via ADP-mediated and inter-domain interactions. Blau syndrome/EOS gain-of-function mutations map to NOD subdomain interfaces and likely disrupt inter-domain interactions to facilitate conformational change to the active form; CD mutations are distributed throughout the protein affecting oligomer formation and ligand binding.\",\n      \"method\": \"X-ray crystallography of ADP-bound NOD2; mutational mapping\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional mutational analysis; high-resolution structural data\",\n      \"pmids\": [\"27283905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"XIAP ubiquitinates RIP2 downstream of NOD2, and the XIAP-RIP2 interaction (via XIAP BIR2 domain) is required for NOD2-mediated NF-κB and MAPK activation and cytokine production. RIP2 kinase activity is dispensable for NOD2 signaling; rather, the RIP2 kinase domain conformation regulates XIAP-BIR2 binding. Specific lysine residues on RIP2 serve as XIAP-dependent ubiquitination sites required for pathway signaling.\",\n      \"method\": \"XIAP antagonists, RIP2 kinase inhibitors, mutagenesis of RIP2 ubiquitination sites, co-immunoprecipitation, NF-κB reporter and cytokine production assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with mutagenesis, pharmacological and genetic tools, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"29452636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Parkin E3 ubiquitin ligase directly interacts with and ubiquitylates NOD2, leading to reduced NOD2 protein levels in astrocytes. Parkin-deficient astrocytes show elevated NOD2 and exaggerated ER stress, JNK activation, and cytokine release; NOD2 knockdown in parkin-deficient astrocytes suppresses these inflammatory defects and protects neighboring neurons.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, siRNA knockdown of parkin and NOD2, co-culture with dopaminergic neurons, cytokine ELISA\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assay, and functional co-culture rescue experiments; single lab\",\n      \"pmids\": [\"30378174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"N-acetylglucosamine kinase (NAGK) is required for MDP (muramyl dipeptide) activation of NOD2. NAGK phosphorylates the N-acetylmuramic acid moiety of MDP at the C6 hydroxyl position, generating 6-O-phospho-MDP, which is the actual NOD2 agonist. Unmodified MDP does not constitutively activate NOD2; NAGK-deficient macrophages are completely defective in MDP sensing.\",\n      \"method\": \"Forward genetic screen, biochemical phosphorylation assay, mass spectrometry identification of 6-O-phospho-MDP, NAGK knockout macrophages, active-site mutagenesis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — forward genetic screen, in vitro biochemical assay with mutagenesis, KO validation; multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"36002575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Blau syndrome gain-of-function NOD2 mutations cluster at two locations in the NACHT domain: the ATP/Mg2+-binding site and helical domain 1. These polymorphisms likely dysregulate ATP hydrolysis and NOD2 autoinhibition, respectively. Complementary mutations in NOD1 do not mirror the NOD2 hyperactivation phenotype, indicating distinct activation/regulation mechanisms for NOD1 and NOD2.\",\n      \"method\": \"Mutational analysis of NOD2 constructs in functional assays; comparative NOD1 mutagenesis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional mutational analysis with comparative NOD1/NOD2 experiments; single lab\",\n      \"pmids\": [\"25093298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NOD2 activation by MDP ordinarily downregulates responses to Toll-like receptor stimulation via induction of IRF4. Cells and mice lacking NOD2 mount increased TLR responses. Administration of MDP to normal mice induces IRF4 and prevents experimental colitis, placing NOD2 as a negative regulator of TLR-driven NF-κB activation through IRF4.\",\n      \"method\": \"NOD2-deficient mice, MDP stimulation assays, NOD2 transgenic mice (increased NOD2 function), IRF4 expression analysis, experimental colitis models (DSS, TNBS)\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO and transgenic mouse models, in vivo colitis models, IRF4 mechanistic link; multiple complementary approaches\",\n      \"pmids\": [\"19079230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Blau syndrome NOD2 mutations in the nucleotide-binding domain reduce canonical RIPK2-mediated NF-κB activation and impair NOD2-mediated cross-regulation of TLR responses. IRF4 upregulation is defective in cells bearing Blau NOD2 mutations, identifying IRF4 as the proximal mediator of NOD2 cross-regulatory suppression of NF-κB. In vivo, mice bearing Blau mutations fail to suppress colitis or arthritis in response to MDP.\",\n      \"method\": \"Overexpression of Blau NOD2 mutants in HEK293 cells, reporter assays, experimental colitis and arthritis models, lentiviral IRF4 transduction rescue, IRF4 expression in patient-derived macrophages\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo functional assays, patient material; single lab but multiple approaches\",\n      \"pmids\": [\"36189261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NOD2 suppresses colorectal tumorigenesis via downregulation of TLR signaling pathways. In vitro, NOD2 activation by MDP inhibits TLR-mediated NF-κB and MAPK activation, associated with induction of IRF4. Nod2-deficient mice show higher NF-κB, ERK, and STAT3 activation during colitis and colorectal tumorigenesis.\",\n      \"method\": \"Nod2-/- mouse colorectal tumorigenesis model, in vitro MDP stimulation with TLR co-stimulation, NF-κB/MAPK/STAT3 activation assays, IRF4 expression analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse model with in vitro mechanistic follow-up; single lab, two complementary approaches\",\n      \"pmids\": [\"28658623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Nod2 is required for controlling commensal bacterial load in the intestinal terminal ileum. Nod2-deficient mice harbor increased commensal bacteria and have diminished ability to prevent intestinal colonization by pathogens. Intestinal crypts from Nod2-/- mice are unable to kill bacteria effectively in vitro. Nod2 expression in the terminal ileum is dependent on the presence of commensal bacteria, establishing a feedback regulatory mechanism.\",\n      \"method\": \"Nod2 knockout mice, bacterial quantification from terminal ilea, in vitro crypt bacterial killing assay, germ-free mouse reconstitution\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse model, germ-free reconstitution, in vitro crypt killing assay; multiple orthogonal methods\",\n      \"pmids\": [\"19805227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NOD2 in intestinal epithelial cells is necessary for LpWJL bacteria-mediated IGF-1 production and postnatal growth promotion in malnourished conventional animals. Muramyl dipeptide and mifamurtide (MDP analogs) are sufficient as NOD2 ligands to stimulate animal growth during undernutrition.\",\n      \"method\": \"Conditional and constitutive Nod2 knockout mice, MDP and mifamurtide administration, IGF-1 measurement, germ-free and conventional malnourished mouse models\",\n      \"journal\": \"Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO localizes function to intestinal epithelial cells, pharmacological ligand validation; single study\",\n      \"pmids\": [\"36821686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In mice, NOD2 is expressed in hypothalamic inhibitory neurons and is activated by muropeptides reaching the brain. Activation of neuronal NOD2 by bacterial peptidoglycan-derived muropeptides regulates appetite and body temperature control, primarily in females.\",\n      \"method\": \"Nod2 knockout mice, live brain imaging, peptidoglycan/muropeptide brain delivery, neuronal activity recording, food intake and body temperature measurement\",\n      \"journal\": \"Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse model with defined neuronal phenotype, peptidoglycan delivery experiment; single study\",\n      \"pmids\": [\"35420957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NOD2 deficiency increases retrograde transport of secretory IgA (SIgA)-pathogen complexes through intestinal M cells by upregulating Dectin-1 and Siglec-5 expression. NOD2 normally downregulates these M cell receptors to limit SIgA retrograde transport.\",\n      \"method\": \"NOD2-deficient human patients and mouse models, M cell receptor expression analysis, SIgA transport assays, receptor KD experiments\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human and mouse loss-of-function data, receptor expression and functional transport assay; single study\",\n      \"pmids\": [\"33431850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"NOD2 exerts anti-tumor effects in hepatocellular carcinoma by directly binding the AMPKα-LKB1 complex, activating AMPK signaling, and triggering autophagy-mediated apoptosis. NOD2 also enhances chemosensitivity to sorafenib, lenvatinib, and 5-FU through AMPK pathway activation.\",\n      \"method\": \"Co-immunoprecipitation of NOD2 with AMPKα-LKB1, Nod2-/- mouse HCC model, xenograft model, in vitro proliferation and invasion assays, AMPK pathway activation assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating direct binding, KO mouse model, multiple cell-based functional assays; single lab\",\n      \"pmids\": [\"32144252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Gut microbial DL-endopeptidase increases the level of NOD2 ligand (muropeptides) in the intestinal lumen. Administration of active DL-endopeptidase, but not an active-site mutant, alleviates colitis via the NOD2 pathway. This establishes that microbially-generated NOD2 ligand availability is a mechanism linking microbiome composition to NOD2-dependent intestinal homeostasis.\",\n      \"method\": \"Metagenomic analysis, active-site DL-endopeptidase mutant control, colitis mouse models (NOD2-dependent rescue), fecal microbiota transplant\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — active-site mutant control establishes enzymatic mechanism, NOD2 KO rescue validates pathway; single study\",\n      \"pmids\": [\"36049483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Activation of NOD2 by its agonist MDP induces CCL5/RANTES secretion from murine macrophages through the NF-κB pathway, not through the interferon-β pathway. In vivo, intraperitoneal injection of NOD2 agonists causes rapid CCL5 secretion into the bloodstream.\",\n      \"method\": \"Murine macrophage stimulation with Nod2 agonists, CCL5 ELISA, NF-κB promoter reporter assay, IFN-β pathway analysis, in vivo peritoneal injection model\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo functional assays, pathway dissection; single lab\",\n      \"pmids\": [\"17705131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"NOD2 stimulation by MDP inhibits odontoblast differentiation of human dental pulp cells through increased MKP-1 protein expression and subsequent dephosphorylation/inactivation of MAPKs required for differentiation. NOD2 siRNA knockdown reverses MDP-mediated inhibition of differentiation.\",\n      \"method\": \"siRNA knockdown of NOD2, ALP activity assay, mineralization assay, MAPK phosphorylation analysis, MKP-1 expression analysis in human dental pulp cells\",\n      \"journal\": \"Journal of dental research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — functional siRNA KD in cell line; single lab, single study\",\n      \"pmids\": [\"24820666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"iPSC-derived macrophages with Blau syndrome NOD2 mutations show IFN-γ-dependent, ligand-independent NF-κB activation and proinflammatory cytokine production. IFN-γ acts as a priming signal by upregulating NOD2 expression, and correction of the NOD2 mutation by CRISPR-Cas9 normalizes inflammatory responses.\",\n      \"method\": \"Blau syndrome-specific iPSC derivation, CRISPR-Cas9 isogenic correction and introduction of NOD2 mutation, iPSC differentiation to macrophages, NF-κB activation assays, cytokine measurements, RNA-seq\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — isogenic CRISPR correction and mutation introduction with multiple orthogonal readouts; rigorous causal mechanistic study\",\n      \"pmids\": [\"28587749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"miR-192, miR-495, miR-512, and miR-671 directly suppress NOD2 expression by targeting its 3'UTR, thereby suppressing MDP-mediated NF-κB activation and IL-8/CXCL3 expression in colonic epithelial cells. A SNP (rs3135500) in the NOD2 3'UTR reduces miR-192 effectiveness.\",\n      \"method\": \"Luciferase reporter constructs with NOD2 3'UTR, miRNA mimic transfection, qRT-PCR, NF-κB reporter assays in HCT116 cells\",\n      \"journal\": \"Inflammatory bowel diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase 3'UTR reporter and functional miRNA overexpression assays with SNP validation; single lab\",\n      \"pmids\": [\"24297055\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NOD2 is an intracellular innate immune pattern recognition receptor that senses bacterial peptidoglycan-derived muramyl dipeptide (specifically after NAGK-mediated phosphorylation to 6-O-phospho-MDP) via its LRR domain, oligomerizes via its NACHT domain in an ADP/ATP-regulated manner, and recruits RIP2/RIPK2 (through CARD-CARD interactions) to activate NF-κB and MAPK pathways via a ubiquitin-dependent cascade involving TRAF6, TAK1, Pellino3, and XIAP-mediated K63-linked ubiquitination of RIP2; negative regulation occurs through TRIM27- and Parkin-mediated K48-linked ubiquitination and proteasomal degradation of NOD2, and through IRF4 induction that suppresses concurrent TLR responses; NOD2 also intersects with ER stress signaling via IRE1α/TRAF2 and promotes autophagy via ATG16L1 to clear intracellular bacteria, while Blau syndrome gain-of-function mutations in the NACHT domain disrupt autoinhibitory inter-domain contacts causing ligand-independent NF-κB activation, and Crohn's disease loss-of-function mutations impair MDP sensing, bacterial killing, defensin expression, microbiota regulation, and IRF4-mediated cross-regulation of TLR responses.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NOD2 is an intracellular innate immune pattern-recognition receptor that senses bacterial peptidoglycan and converts this detection into NF-\\u03baB- and MAPK-driven inflammatory and antibacterial responses, originally established through loss-of-function frameshift mutation (3020insC) that abrogates NF-\\u03baB activation [#0]. The proximal agonist is not muramyl dipeptide (MDP) itself but 6-O-phospho-MDP, generated when NAGK phosphorylates the N-acetylmuramic acid moiety; NAGK-deficient macrophages are completely defective in MDP sensing [#12]. Crystallographic analysis of ADP-bound NOD2 shows a closed, autoinhibited conformation maintained by inter-domain and nucleotide-mediated contacts within the NOD/NACHT domain [#9]. Upon activation, NOD2 signals through RIP2/RIPK2, whose K63-linked polyubiquitination by TRAF6/Ubc13 with TAK1, by the E3 ligase Pellino3, and by XIAP (via its BIR2 domain) drives downstream IKK\\u03b3 ubiquitination and NF-\\u03baB/MAPK activation; RIP2 kinase activity is dispensable, serving instead to position the kinase domain for XIAP binding [#1, #6, #10]. Beyond canonical inflammation, NOD2 couples MDP sensing to ATG16L1-dependent autophagy for intracellular bacterial killing, and Crohn's-associated NOD2 variants impair this response [#4]. NOD2 also acts as a negative regulator, dampening Toll-like-receptor-driven NF-\\u03baB through induction of IRF4, a cross-regulatory function important for restraining colitis and colorectal tumorigenesis [#14, #16]. NOD2 protein levels are tightly controlled by E3 ligases TRIM27 and Parkin, which catalyze K48-linked ubiquitination and proteasomal degradation, while p62/SQSTM1 stabilizes NOD2 oligomers [#5, #7, #11]. In vivo, NOD2 controls commensal bacterial load and crypt antibacterial killing in the terminal ileum, where its expression itself depends on the microbiota [#17]. Gain-of-function mutations in the NACHT domain cause Blau syndrome through ligand-independent, IFN-\\u03b3-primed NF-\\u03baB activation [#13, #25].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established NOD2 as an innate immune sensor functioning upstream of NF-\\u03baB, with a disease-associated truncating mutation defining loss of function.\",\n      \"evidence\": \"NF-\\u03baB reporter assays comparing wild-type versus 3020insC mutant NOD2, plus genetic association analysis\",\n      \"pmids\": [\"11385577\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the precise physiological ligand\", \"Did not define the downstream adaptor/effector cascade\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identified TAK1 as a NOD2-interacting kinase required for MDP-induced NF-\\u03baB, revealing reciprocal cross-talk via the LRR domain.\",\n      \"evidence\": \"Co-IP, dominant-negative TAK1, and NF-\\u03baB reporter assays in RICK-deficient fibroblasts\",\n      \"pmids\": [\"15075345\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of LRR-mediated inhibition not structurally resolved\", \"Single-lab Co-IP without reciprocal genetic validation\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the ubiquitin-dependent core of NOD2 signaling, showing K63-linked polyubiquitination of RIP2 is required for IKK\\u03b3 ubiquitination and NF-\\u03baB activation.\",\n      \"evidence\": \"In vitro ubiquitination assays, Co-IP, knockdown/dominant-negative in M. tuberculosis-infected and MDP-treated macrophages\",\n      \"pmids\": [\"17947236\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether multiple E3 ligases act redundantly\", \"Site-specific RIP2 ubiquitination not yet mapped\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed NOD2 activation produces a specific chemokine output (CCL5/RANTES) through NF-\\u03baB rather than the interferon-\\u03b2 pathway.\",\n      \"evidence\": \"Murine macrophage MDP stimulation, CCL5 ELISA, NF-\\u03baB reporter, and in vivo injection\",\n      \"pmids\": [\"17705131\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Scope of NOD2-driven chemokine repertoire not defined\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Reframed NOD2 as a negative regulator of innate immunity by showing MDP-induced IRF4 suppresses TLR-driven NF-\\u03baB and prevents experimental colitis.\",\n      \"evidence\": \"NOD2-deficient and transgenic mice, MDP stimulation, IRF4 analysis, DSS/TNBS colitis models\",\n      \"pmids\": [\"19079230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which NOD2 induces IRF4 not detailed\", \"Cell-type-specific contributions not separated\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established an in vivo physiological role for NOD2 in controlling commensal load and crypt antibacterial killing, with a microbiota-dependent expression feedback loop.\",\n      \"evidence\": \"Nod2 knockout mice, terminal ileum bacterial quantification, in vitro crypt killing, germ-free reconstitution\",\n      \"pmids\": [\"19805227\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effector mechanism of crypt killing (e.g. specific antimicrobials) not resolved here\", \"Direct link to human disease variants not tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected NOD2 sensing to autophagy-mediated bacterial clearance via ATG16L1 and showed Crohn's variants impair this antibacterial arm.\",\n      \"evidence\": \"Gentamicin protection, confocal microscopy, RNAi of NOD2/ATG16L1, primary cells from genotyped donors\",\n      \"pmids\": [\"20637199\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between NOD2 and ATG16L1 recruitment not fully defined\", \"Relative contribution of autophagy versus NF-\\u03baB arm not quantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified TRIM27 as an E3 ligase that terminates NOD2 signaling via K48-linked ubiquitination and proteasomal degradation.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, proteasome inhibition, reporter assays in HeLa\",\n      \"pmids\": [\"22829933\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance not tested\", \"Single-lab overexpression system\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Added Pellino3 as a positive E3 ligase ubiquitinating RIP2 downstream of NOD2, with an in vivo colitis phenotype.\",\n      \"evidence\": \"Co-IP, in vitro ubiquitination, Pellino3 knockout mice, colitis models\",\n      \"pmids\": [\"23892723\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Hierarchy among RIP2 E3 ligases (TRAF6, Pellino3, XIAP) unresolved\", \"Ubiquitin chain linkage specificity not fully detailed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed p62/SQSTM1 positively regulates NOD2 by stabilizing oligomerization and preventing degradation.\",\n      \"evidence\": \"Co-IP, electron microscopy of NOD2-p62 complex, NF-\\u03baB reporter, cytokine ELISA\",\n      \"pmids\": [\"23437331\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo requirement not established\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Localized Blau syndrome gain-of-function mutations to the ATP/Mg2+-binding site and helical domain 1 of the NACHT domain, distinguishing NOD2 activation/regulation from NOD1.\",\n      \"evidence\": \"Mutational functional analysis of NOD2 constructs with comparative NOD1 mutagenesis\",\n      \"pmids\": [\"25093298\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural mechanism inferred not directly visualized\", \"Single-lab functional assays\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated post-transcriptional control of NOD2 by multiple miRNAs targeting its 3'UTR, with a disease-associated SNP modulating miRNA efficacy.\",\n      \"evidence\": \"3'UTR luciferase reporters, miRNA mimics, NF-\\u03baB reporters in colonic epithelial cells\",\n      \"pmids\": [\"24297055\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological/in vivo relevance not tested\", \"Relative dominance among the four miRNAs unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Extended NOD2 signaling beyond immunity to inhibition of odontoblast differentiation via MKP-1-mediated MAPK inactivation.\",\n      \"evidence\": \"siRNA knockdown, differentiation and mineralization assays, MAPK/MKP-1 analysis in dental pulp cells\",\n      \"pmids\": [\"24820666\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single-lab cell-line study not independently confirmed\", \"No in vivo validation\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Provided the structural basis of NOD2 autoinhibition, showing an ADP-bound closed conformation whose interfaces are disrupted by Blau gain-of-function mutations.\",\n      \"evidence\": \"X-ray crystallography of ADP-bound rabbit NOD2 with mutational mapping\",\n      \"pmids\": [\"27283905\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Active oligomeric (ligand-bound) state not captured\", \"LRR-ligand engagement not visualized in this structure\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Linked NOD2 to ER stress signaling, showing physical association with IRE1\\u03b1/TRAF2 and requirement for ER-stress- and infection-induced inflammation.\",\n      \"evidence\": \"Genetic KO/KD cells, IRE1\\u03b1 kinase inhibitor, Brucella infection model, cytokine and NF-\\u03baB assays\",\n      \"pmids\": [\"27007849\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ER stress sensing requires peptidoglycan ligand unclear\", \"Direct NOD2-IRE1\\u03b1 interaction interface not mapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated NOD2 suppresses colorectal tumorigenesis through IRF4-associated downregulation of TLR/NF-\\u03baB/MAPK/STAT3 signaling.\",\n      \"evidence\": \"Nod2-/- colorectal tumor model with in vitro MDP/TLR co-stimulation\",\n      \"pmids\": [\"28658623\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal role of IRF4 in tumor suppression not directly tested\", \"Epithelial versus immune cell contribution unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established causal, mutation-specific Blau syndrome mechanism: ligand-independent NF-\\u03baB activation requiring IFN-\\u03b3 priming, reversible by isogenic CRISPR correction.\",\n      \"evidence\": \"Blau patient iPSC-derived macrophages, CRISPR isogenic correction/introduction, NF-\\u03baB and cytokine assays, RNA-seq\",\n      \"pmids\": [\"28587749\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of IFN-\\u03b3-driven NOD2 priming not fully dissected\", \"Generalizability across Blau mutations not exhaustively tested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined XIAP as an essential RIP2 E3 ligase acting via its BIR2 domain and showed RIP2 kinase activity is dispensable, with the kinase domain conformation regulating XIAP binding.\",\n      \"evidence\": \"XIAP antagonists, RIP2 kinase inhibitors, ubiquitination-site mutagenesis, Co-IP, reporter and cytokine assays\",\n      \"pmids\": [\"29452636\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional hierarchy with TRAF6/Pellino3 not reconciled\", \"Structural basis of kinase-domain/BIR2 coupling not solved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed Parkin ubiquitylates and degrades NOD2 in astrocytes, linking NOD2 dysregulation to neuroinflammation and neuronal toxicity.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, parkin/NOD2 siRNA, dopaminergic neuron co-culture rescue\",\n      \"pmids\": [\"30378174\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo neurodegeneration relevance not established\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified a non-immune, anti-tumor function of NOD2 in hepatocellular carcinoma through direct binding to the AMPK\\u03b1-LKB1 complex and autophagy-mediated apoptosis.\",\n      \"evidence\": \"Co-IP, Nod2-/- HCC and xenograft models, AMPK pathway and proliferation/invasion assays\",\n      \"pmids\": [\"32144252\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this is peptidoglycan-ligand dependent unclear\", \"Single-lab mechanistic study\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed NOD2 controls intestinal M-cell receptor expression, limiting retrograde transport of SIgA-pathogen complexes by suppressing Dectin-1 and Siglec-5.\",\n      \"evidence\": \"Human NOD2-deficient patients and mouse models, M-cell receptor expression and SIgA transport assays\",\n      \"pmids\": [\"33431850\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling pathway linking NOD2 to receptor repression undefined\", \"Single study\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Redefined the true NOD2 agonist by showing NAGK phosphorylates MDP to 6-O-phospho-MDP, which is required for NOD2 activation.\",\n      \"evidence\": \"Forward genetic screen, biochemical phosphorylation assay, mass spectrometry, NAGK-KO macrophages, active-site mutagenesis\",\n      \"pmids\": [\"36002575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of 6-O-phospho-MDP recognition by NOD2 LRR not solved\", \"Whether all NOD2 ligands require NAGK modification unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed Blau NACHT mutations paradoxically impair canonical RIPK2 signaling and IRF4-mediated cross-regulation, identifying IRF4 as the proximal mediator of NOD2 suppression of TLR/NF-\\u03baB in vivo.\",\n      \"evidence\": \"Blau mutant overexpression, reporter assays, colitis/arthritis models, lentiviral IRF4 rescue, patient macrophages\",\n      \"pmids\": [\"36189261\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation with gain-of-function inflammatory phenotype not fully clarified\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated microbial DL-endopeptidase availability controls luminal NOD2 ligand levels, linking microbiome enzymatic activity to NOD2-dependent intestinal homeostasis.\",\n      \"evidence\": \"Metagenomics, active-site mutant control, NOD2-dependent colitis rescue, fecal transplant\",\n      \"pmids\": [\"36049483\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the specific muropeptide species not fully defined\", \"Single study\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended NOD2 function to systemic physiology, showing intestinal epithelial NOD2 mediates microbiota-driven IGF-1 production and postnatal growth during undernutrition.\",\n      \"evidence\": \"Conditional and constitutive Nod2 KO mice, MDP/mifamurtide administration, IGF-1 measurement, germ-free models\",\n      \"pmids\": [\"36821686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling pathway from epithelial NOD2 to IGF-1 not detailed\", \"Single study\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified a neuronal role for NOD2 in hypothalamic inhibitory neurons regulating appetite and body temperature in response to bacterial muropeptides.\",\n      \"evidence\": \"Nod2 KO mice, live brain imaging, muropeptide brain delivery, neuronal recording, food intake/temperature measurement\",\n      \"pmids\": [\"35420957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream neuronal signaling pathway undefined\", \"Sex-specific mechanism not explained\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ligand-bound NOD2 transitions from the autoinhibited ADP-bound state to an active oligomer that recruits RIP2, and how the competing positive and negative ubiquitin E3 ligases are coordinated in time and tissue, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the active, ligand-engaged NOD2 oligomer\", \"Functional hierarchy among TRAF6, Pellino3, XIAP, TRIM27, and Parkin not integrated\", \"Mechanism connecting NOD2 to ATG16L1, IRF4, and AMPK arms not unified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [9, 13]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [0, 12]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [14, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 14, 17]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 10]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [4, 21]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [5, 11, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"RIPK2\", \"MAP3K7\", \"TRAF6\", \"XIAP\", \"TRIM27\", \"PARK2\", \"SQSTM1\", \"ERN1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}