{"gene":"MAP3K21","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2016,"finding":"MLK4 binds and directly phosphorylates IKKα (CHUK), leading to activation of NF-κB signaling in glioma stem cells and driving mesenchymal identity, self-renewal, motility, and radioresistance.","method":"Co-immunoprecipitation (binding), kinase phosphorylation assay (IKKα phosphorylation), MLK4 silencing with loss-of-MES-signature phenotypic readout","journal":"Cancer Cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal binding assay plus direct phosphorylation assay plus loss-of-function phenotypic rescue, single lab with multiple orthogonal methods","pmids":["26859459"],"is_preprint":false},{"year":2015,"finding":"MLK4 loss-of-function mutations in colon cancer suppress the JNK signaling pathway; restoring MLK4 activity selectively induced JNK pathway activation and downstream targets cJUN, ATF3, CDKN1A, and CDKN2B, reducing cell viability and tumor growth. A new MLK4 catalytic domain crystal structure was elucidated to explain mutant inactivity.","method":"Reconstitution of signaling axis in cancer cells with MLK4-inactivating mutations, kinase activity assays, crystal structure of catalytic domain, in vitro and in vivo tumor growth assays","journal":"Cancer Research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus biochemical reconstitution plus in vivo validation, single lab with multiple orthogonal methods","pmids":["26637668"],"is_preprint":false},{"year":2013,"finding":"MLK4 directly phosphorylates MEK1 (MAP2K1), and MEK/ERK signaling is impaired in MLK4 knockout cells; MLK4-mutated alleles in CRC are constitutively active and cooperate with activated RAS to drive tumorigenesis.","method":"Direct phosphorylation assay (MEK1), MLK4 knockout cell lines, in vitro transformation assays, xenograft models","journal":"Cancer Research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct kinase-substrate phosphorylation assay combined with KO cells and in vivo validation, single lab with multiple orthogonal methods","pmids":["23319808"],"is_preprint":false},{"year":2011,"finding":"MLK4 interacts with TLR4 and acts as a negative regulator of TLR4 signaling: MLK4 inhibits LPS-induced JNK and ERK activation and reduces TNF-α production, while MLK4 knockdown increases and overexpression reduces LPS-induced TNF production. Unlike other MLK family members, MLK4 cannot activate JNK, p38, or ERK as a MAP3K.","method":"Co-immunoprecipitation (TLR4 interaction), MLK4 knockdown and overexpression in macrophages, LPS stimulation assays measuring JNK/ERK/p38/NF-κB activation and TNF-α production","journal":"Cellular & Molecular Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus functional gain/loss-of-function with cytokine readout, single lab","pmids":["21602844"],"is_preprint":false},{"year":2021,"finding":"MLK4 promotes DNA damage response in TNBC by regulating phosphorylation of ATM and CHK2, and supports DNA repair via non-homologous end-joining (NHEJ). MLK4 is also required for DNA damage-induced NF-κB-associated cytokine expression that facilitates cell survival.","method":"MLK4 knockdown and inhibition, phosphoproteomic profiling, reporter assays (NF-κB), mRNA-seq, in vivo doxorubicin sensitivity assay","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phosphoproteomic profiling plus reporter assays plus in vivo validation, single lab with multiple orthogonal methods","pmids":["34839359"],"is_preprint":false},{"year":2018,"finding":"MLK4 activates NF-κB signaling and promotes a mesenchymal phenotype in breast cancer cells, driving migratory and invasive potential.","method":"MLK4 silencing (siRNA/shRNA), NF-κB reporter assays, migration/invasion assays, 3D spheroid assays, in vivo xenograft","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined cellular phenotypes and pathway readout, in vitro and in vivo, single lab","pmids":["30552384"],"is_preprint":false},{"year":2023,"finding":"MLK4 phosphorylates the transcription factor CREB, which in turn drives transcriptional activation of PCK1 (phosphoenolpyruvate carboxykinase 1), linking MLK4 kinase activity to regulation of glycolytic metabolism in lung adenocarcinoma. KLF5 transcription factor binds the MLK4 promoter and positively regulates MLK4 expression.","method":"Phosphorylation assay (CREB), transcriptional reporter/promoter analysis, metabolic assays (glycolysis, mass spectrometry metabolite profiling), MLK4 knockdown","journal":"Oncogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct phosphorylation assay plus promoter analysis plus metabolomic validation, single lab","pmids":["37407566"],"is_preprint":false},{"year":2025,"finding":"IL-17RB interacts with MLK4 through cysteine 408 of IL-17RB and arginine 216 within the MLK4 kinase domain; disruption of this protein-protein interaction with a cyclic peptide inhibited pancreatic cancer cell growth and metastasis.","method":"Peptide-based protein-protein interaction disruption assay, site-directed mutagenesis (C408 in IL-17RB, R216 in MLK4), in vitro growth/metastasis assays, orthotopic mouse model","journal":"Biomedicine & Pharmacotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis mapping of interaction residues plus in vitro and in vivo functional validation, single lab","pmids":["39913969"],"is_preprint":false},{"year":2026,"finding":"In TNBC, MLK4 mediates macrophage-induced cancer cell proliferation, ECM remodeling, migration, and invasion through activation of NF-κB and downstream matrix metalloproteinase (MMP) expression; MLK4-dependent paracrine signaling prominently upregulates CXCL1 and IL-8 in TNBC–macrophage co-culture.","method":"TNBC–macrophage co-culture system, MLK4 depletion, NF-κB activity assays, MMP expression profiling, migration/invasion assays","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function in co-culture model with defined molecular pathway readout, single lab","pmids":["41922320"],"is_preprint":false},{"year":2019,"finding":"MLK4 knockdown in HCC cells elevated reactive oxygen species (ROS) production and increased phosphorylation of p38, JNK, and ERK1/2; blocking ROS generation or MAPKs signaling rescued the apoptosis and anti-metastatic effects caused by MLK4 silencing, placing MLK4 upstream of ROS/MAPKs in HCC.","method":"MLK4 siRNA knockdown, ROS measurement, Western blot for phospho-p38/JNK/ERK, pharmacological rescue with ROS scavengers and MAPK inhibitors, xenograft and metastasis models","journal":"Biomedicine & Pharmacotherapy","confidence":"Low","confidence_rationale":"Tier 3 / Weak — indirect upstream placement via pharmacological rescue, single lab, single method type","pmids":["31071576"],"is_preprint":false}],"current_model":"MAP3K21/MLK4 is a serine/threonine kinase that functions as an upstream MAP3K: it directly phosphorylates IKKα to activate NF-κB signaling, phosphorylates MEK1 to activate ERK, phosphorylates CREB to drive transcriptional targets including PCK1, and activates the JNK pathway; loss-of-function mutations in colon cancer suppress JNK signaling and reduce tumor-suppressive outputs, while gain-of-function in glioma and breast cancer drives NF-κB-dependent mesenchymal identity, DNA damage resistance, and invasiveness; MLK4 also interacts with TLR4 to negatively regulate LPS-induced JNK/ERK activation and TNF production, and its kinase domain engages IL-17RB through a defined R216–C408 interface to mediate oncogenic signaling in pancreatic cancer."},"narrative":{"mechanistic_narrative":"MAP3K21 (MLK4) is a serine/threonine MAP3K-family kinase that integrates upstream signals into NF-κB, MAPK, and CREB transcriptional outputs to control cancer cell identity, survival, and invasion [PMID:26859459, PMID:23319808, PMID:37407566]. Its best-defined biochemical activity is direct substrate phosphorylation: MLK4 binds and phosphorylates IKKα to activate NF-κB signaling that drives mesenchymal identity, self-renewal, motility, and radioresistance in glioma stem cells [PMID:26859459], and phosphorylates MEK1 to engage the MEK/ERK axis, with MLK4-mutant alleles acting as constitutively active drivers that cooperate with activated RAS in colorectal cancer [PMID:23319808]. MLK4 also phosphorylates the transcription factor CREB to induce PCK1 and reprogram glycolytic metabolism, with its own expression positively controlled by KLF5 [PMID:37407566]. The kinase exerts context-dependent and opposing effects on the JNK pathway: loss-of-function mutations in colon cancer suppress JNK signaling, and restoring MLK4 activity reactivates JNK targets cJUN, ATF3, CDKN1A, and CDKN2B to limit tumor growth, a behavior rationalized by a catalytic-domain crystal structure explaining mutant inactivity [PMID:26637668]. In breast cancer, MLK4 activates NF-κB to promote mesenchymal, migratory, and invasive phenotypes [PMID:30552384], supports the DNA damage response through ATM/CHK2 phosphorylation and NHEJ-mediated repair [PMID:34839359], and mediates macrophage-induced proliferation and ECM remodeling via NF-κB-driven MMP, CXCL1, and IL-8 expression [PMID:41922320]. Beyond its oncogenic kinase activities, MLK4 interacts with TLR4 to negatively regulate LPS-induced JNK/ERK activation and TNF-α production in macrophages [PMID:21602844], and engages IL-17RB through a defined R216–C408 interface that supports pancreatic cancer growth and metastasis [PMID:39913969].","teleology":[{"year":2011,"claim":"Established the first signaling partner and an unexpectedly negative regulatory role, distinguishing MLK4 from other MLK-family MAP3Ks that activate stress kinases.","evidence":"Co-IP of TLR4, plus knockdown/overexpression in macrophages with LPS-induced cytokine and MAPK readouts","pmids":["21602844"],"confidence":"Medium","gaps":["Did not identify the direct substrate through which MLK4 dampens TLR4 signaling","Whether kinase activity is required for the negative-regulatory effect was not resolved"]},{"year":2013,"claim":"Identified MEK1 as a direct MLK4 substrate and showed cancer-associated alleles are constitutively active, framing MLK4 as a RAS-cooperating oncogenic kinase.","evidence":"Direct MEK1 phosphorylation assay, MLK4 knockout cells, transformation and xenograft assays","pmids":["23319808"],"confidence":"High","gaps":["Did not reconcile activating CRC alleles here with loss-of-function CRC alleles reported elsewhere","Structural basis of constitutive activation not defined"]},{"year":2015,"claim":"Resolved a context where MLK4 is tumor-suppressive via JNK, and provided a catalytic-domain structure explaining how mutations inactivate the kinase.","evidence":"Reconstitution of MLK4 activity in mutant CRC cells, kinase assays, catalytic-domain crystal structure, in vivo tumor growth","pmids":["26637668"],"confidence":"High","gaps":["Did not define which upstream signals select JNK versus MEK/ERK or NF-κB output","Mechanistic basis for opposite mutational consequences across cancers unresolved"]},{"year":2016,"claim":"Defined the IKKα–NF-κB axis as the route by which MLK4 enforces mesenchymal identity and radioresistance in glioma stem cells.","evidence":"Reciprocal Co-IP, direct IKKα phosphorylation assay, MLK4 silencing with mesenchymal-signature phenotypic readout","pmids":["26859459"],"confidence":"High","gaps":["Upstream activators recruiting MLK4 to IKKα not identified","Selectivity for IKKα over other IKK subunits not addressed"]},{"year":2018,"claim":"Extended the NF-κB-driven mesenchymal program from glioma to breast cancer invasion.","evidence":"MLK4 silencing, NF-κB reporter, migration/invasion and 3D spheroid assays, xenograft","pmids":["30552384"],"confidence":"Medium","gaps":["Direct substrate in breast cancer NF-κB activation not confirmed","Downstream effector genes not enumerated"]},{"year":2019,"claim":"Placed MLK4 upstream of a ROS/MAPK survival axis in hepatocellular carcinoma, with MLK4 loss promoting apoptosis.","evidence":"siRNA knockdown, ROS measurement, phospho-MAPK blots, pharmacological rescue, xenograft/metastasis models","pmids":["31071576"],"confidence":"Low","gaps":["Upstream placement is indirect, inferred from pharmacological rescue rather than direct biochemistry","No direct MLK4 substrate identified in this pathway","Single method type, not independently confirmed"]},{"year":2021,"claim":"Connected MLK4 to genome maintenance, showing it promotes ATM/CHK2-mediated DNA damage response and NHEJ repair to support survival in TNBC.","evidence":"MLK4 knockdown/inhibition, phosphoproteomics, NF-κB reporter, mRNA-seq, in vivo doxorubicin sensitivity","pmids":["34839359"],"confidence":"Medium","gaps":["Whether MLK4 directly phosphorylates ATM/CHK2 or acts indirectly not resolved","Mechanistic link between NF-κB cytokine output and repair not dissected"]},{"year":2023,"claim":"Added a metabolic output by showing MLK4 phosphorylates CREB to drive PCK1 and glycolytic reprogramming, and identified KLF5 as a transcriptional activator of MLK4.","evidence":"CREB phosphorylation assay, promoter/reporter analysis, metabolomic profiling, knockdown","pmids":["37407566"],"confidence":"Medium","gaps":["Whether CREB phosphorylation is direct versus relayed not fully established","Generality of the CREB–PCK1 axis beyond lung adenocarcinoma untested"]},{"year":2025,"claim":"Mapped a druggable IL-17RB–MLK4 interface (IL-17RB C408 / MLK4 R216), establishing a protein-protein interaction route to oncogenic signaling in pancreatic cancer.","evidence":"Site-directed mutagenesis of interface residues, cyclic-peptide disruption, in vitro and orthotopic in vivo growth/metastasis assays","pmids":["39913969"],"confidence":"Medium","gaps":["Downstream signaling triggered by the IL-17RB–MLK4 interaction not delineated","Whether the interaction modulates MLK4 catalytic activity unknown"]},{"year":2026,"claim":"Showed MLK4 mediates tumor–macrophage crosstalk, driving NF-κB-dependent MMP, CXCL1, and IL-8 to promote ECM remodeling and invasion in TNBC.","evidence":"TNBC–macrophage co-culture, MLK4 depletion, NF-κB assays, MMP profiling, migration/invasion assays","pmids":["41922320"],"confidence":"Medium","gaps":["Direct substrate linking macrophage cues to MLK4 activation not identified","Receptor relaying macrophage signal to MLK4 not defined"]},{"year":null,"claim":"It remains unresolved how a single kinase produces opposing outputs—tumor-suppressive JNK activation versus oncogenic NF-κB/ERK signaling—and what upstream receptors and contextual cues dictate substrate selection.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model of context-dependent substrate choice","Physiological (non-cancer) function and endogenous activators largely uncharacterized in the corpus","Whether IL-17RB and TLR4 engagement converge on the same catalytic outputs unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,6]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,2,6]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[6]}],"localization":[],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,3]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,2,5,7,8]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[4]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,8]}],"complexes":[],"partners":["CHUK","MAP2K1","TLR4","IL17RB","CREB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5TCX8","full_name":"Mitogen-activated protein kinase kinase kinase 21","aliases":["Mitogen-activated protein kinase kinase kinase MLK4","Mixed lineage kinase 4"],"length_aa":1036,"mass_kda":114.0,"function":"Negative regulator of TLR4 signaling. Does not activate JNK1/MAPK8 pathway, p38/MAPK14, nor ERK2/MAPK1 pathways","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q5TCX8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MAP3K21","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CLTA","stoichiometry":0.2},{"gene":"DNAJB6","stoichiometry":0.2},{"gene":"DNAJC7","stoichiometry":0.2},{"gene":"FKBP5","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/MAP3K21","total_profiled":1310},"omim":[{"mim_id":"614793","title":"MITOGEN-ACTIVATED PROTEIN KINASE KINASE KINASE 21; MAP3K21","url":"https://www.omim.org/entry/614793"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"pancreas","ntpm":19.1}],"url":"https://www.proteinatlas.org/search/MAP3K21"},"hgnc":{"alias_symbol":["KIAA1804","MLK4"],"prev_symbol":[]},"alphafold":{"accession":"Q5TCX8","domains":[{"cath_id":"2.30.30.40","chopping":"43-100","consensus_level":"high","plddt":88.4491,"start":43,"end":100},{"cath_id":"3.30.200.20","chopping":"115-203","consensus_level":"medium","plddt":88.6846,"start":115,"end":203},{"cath_id":"1.10.510.10","chopping":"208-220_229-293_305-439","consensus_level":"medium","plddt":90.379,"start":208,"end":439}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5TCX8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5TCX8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5TCX8-F1-predicted_aligned_error_v6.png","plddt_mean":58.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MAP3K21","jax_strain_url":"https://www.jax.org/strain/search?query=MAP3K21"},"sequence":{"accession":"Q5TCX8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5TCX8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5TCX8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5TCX8"}},"corpus_meta":[{"pmid":"26859459","id":"PMC_26859459","title":"Serine/Threonine Kinase MLK4 Determines Mesenchymal Identity in Glioma Stem Cells in an NF-κB-dependent Manner.","date":"2016","source":"Cancer cell","url":"https://pubmed.ncbi.nlm.nih.gov/26859459","citation_count":143,"is_preprint":false},{"pmid":"26637668","id":"PMC_26637668","title":"Recurrent MLK4 Loss-of-Function Mutations Suppress JNK Signaling to Promote Colon Tumorigenesis.","date":"2015","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/26637668","citation_count":30,"is_preprint":false},{"pmid":"21602844","id":"PMC_21602844","title":"MLK4 has negative effect on TLR4 signaling.","date":"2011","source":"Cellular & molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/21602844","citation_count":28,"is_preprint":false},{"pmid":"34839359","id":"PMC_34839359","title":"MLK4 regulates DNA damage response and promotes triple-negative breast cancer chemoresistance.","date":"2021","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/34839359","citation_count":25,"is_preprint":false},{"pmid":"30552384","id":"PMC_30552384","title":"Upregulation of MLK4 promotes migratory and invasive potential of breast cancer cells.","date":"2018","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/30552384","citation_count":21,"is_preprint":false},{"pmid":"23319808","id":"PMC_23319808","title":"Mixed lineage kinase MLK4 is activated in colorectal cancers where it synergistically cooperates with activated RAS signaling in driving tumorigenesis.","date":"2013","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/23319808","citation_count":18,"is_preprint":false},{"pmid":"31071576","id":"PMC_31071576","title":"Decrease of MLK4 prevents hepatocellular carcinoma (HCC) through reducing metastasis and inducing apoptosis regulated by ROS/MAPKs signaling.","date":"2019","source":"Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/31071576","citation_count":16,"is_preprint":false},{"pmid":"37407566","id":"PMC_37407566","title":"MLK4 promotes glucose metabolism in lung adenocarcinoma through CREB-mediated activation of phosphoenolpyruvate carboxykinase and is regulated by KLF5.","date":"2023","source":"Oncogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/37407566","citation_count":7,"is_preprint":false},{"pmid":"39298888","id":"PMC_39298888","title":"Discovery of novel MLK4 inhibitors against colorectal cancer through computational approaches.","date":"2024","source":"Computers in biology and medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39298888","citation_count":5,"is_preprint":false},{"pmid":"39913969","id":"PMC_39913969","title":"Innovative cyclic peptide disrupts IL-17RB-MLK4 interaction for targeted pancreatic cancer therapy.","date":"2025","source":"Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/39913969","citation_count":2,"is_preprint":false},{"pmid":"41922320","id":"PMC_41922320","title":"MLK4 orchestrates macrophage-induced triple-negative breast cancer invasion and ECM remodeling via enhanced paracrine signaling and NF-κB-MMP axis activation.","date":"2026","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/41922320","citation_count":0,"is_preprint":false},{"pmid":"42068033","id":"PMC_42068033","title":"Integrated 2D-3D Proteomic Profiling Identifies MLK4 as a Microenvironment-Responsive Regulator of Chemotherapeutic Resistance in Human Glioblastoma Cells.","date":"2026","source":"Biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/42068033","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8040,"output_tokens":2591,"usd":0.031492,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9843,"output_tokens":3734,"usd":0.071282,"stage2_stop_reason":"end_turn"},"total_usd":0.102774,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2016,\n      \"finding\": \"MLK4 binds and directly phosphorylates IKKα (CHUK), leading to activation of NF-κB signaling in glioma stem cells and driving mesenchymal identity, self-renewal, motility, and radioresistance.\",\n      \"method\": \"Co-immunoprecipitation (binding), kinase phosphorylation assay (IKKα phosphorylation), MLK4 silencing with loss-of-MES-signature phenotypic readout\",\n      \"journal\": \"Cancer Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding assay plus direct phosphorylation assay plus loss-of-function phenotypic rescue, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"26859459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MLK4 loss-of-function mutations in colon cancer suppress the JNK signaling pathway; restoring MLK4 activity selectively induced JNK pathway activation and downstream targets cJUN, ATF3, CDKN1A, and CDKN2B, reducing cell viability and tumor growth. A new MLK4 catalytic domain crystal structure was elucidated to explain mutant inactivity.\",\n      \"method\": \"Reconstitution of signaling axis in cancer cells with MLK4-inactivating mutations, kinase activity assays, crystal structure of catalytic domain, in vitro and in vivo tumor growth assays\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus biochemical reconstitution plus in vivo validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"26637668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MLK4 directly phosphorylates MEK1 (MAP2K1), and MEK/ERK signaling is impaired in MLK4 knockout cells; MLK4-mutated alleles in CRC are constitutively active and cooperate with activated RAS to drive tumorigenesis.\",\n      \"method\": \"Direct phosphorylation assay (MEK1), MLK4 knockout cell lines, in vitro transformation assays, xenograft models\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct kinase-substrate phosphorylation assay combined with KO cells and in vivo validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"23319808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MLK4 interacts with TLR4 and acts as a negative regulator of TLR4 signaling: MLK4 inhibits LPS-induced JNK and ERK activation and reduces TNF-α production, while MLK4 knockdown increases and overexpression reduces LPS-induced TNF production. Unlike other MLK family members, MLK4 cannot activate JNK, p38, or ERK as a MAP3K.\",\n      \"method\": \"Co-immunoprecipitation (TLR4 interaction), MLK4 knockdown and overexpression in macrophages, LPS stimulation assays measuring JNK/ERK/p38/NF-κB activation and TNF-α production\",\n      \"journal\": \"Cellular & Molecular Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus functional gain/loss-of-function with cytokine readout, single lab\",\n      \"pmids\": [\"21602844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MLK4 promotes DNA damage response in TNBC by regulating phosphorylation of ATM and CHK2, and supports DNA repair via non-homologous end-joining (NHEJ). MLK4 is also required for DNA damage-induced NF-κB-associated cytokine expression that facilitates cell survival.\",\n      \"method\": \"MLK4 knockdown and inhibition, phosphoproteomic profiling, reporter assays (NF-κB), mRNA-seq, in vivo doxorubicin sensitivity assay\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphoproteomic profiling plus reporter assays plus in vivo validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"34839359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MLK4 activates NF-κB signaling and promotes a mesenchymal phenotype in breast cancer cells, driving migratory and invasive potential.\",\n      \"method\": \"MLK4 silencing (siRNA/shRNA), NF-κB reporter assays, migration/invasion assays, 3D spheroid assays, in vivo xenograft\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined cellular phenotypes and pathway readout, in vitro and in vivo, single lab\",\n      \"pmids\": [\"30552384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MLK4 phosphorylates the transcription factor CREB, which in turn drives transcriptional activation of PCK1 (phosphoenolpyruvate carboxykinase 1), linking MLK4 kinase activity to regulation of glycolytic metabolism in lung adenocarcinoma. KLF5 transcription factor binds the MLK4 promoter and positively regulates MLK4 expression.\",\n      \"method\": \"Phosphorylation assay (CREB), transcriptional reporter/promoter analysis, metabolic assays (glycolysis, mass spectrometry metabolite profiling), MLK4 knockdown\",\n      \"journal\": \"Oncogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct phosphorylation assay plus promoter analysis plus metabolomic validation, single lab\",\n      \"pmids\": [\"37407566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IL-17RB interacts with MLK4 through cysteine 408 of IL-17RB and arginine 216 within the MLK4 kinase domain; disruption of this protein-protein interaction with a cyclic peptide inhibited pancreatic cancer cell growth and metastasis.\",\n      \"method\": \"Peptide-based protein-protein interaction disruption assay, site-directed mutagenesis (C408 in IL-17RB, R216 in MLK4), in vitro growth/metastasis assays, orthotopic mouse model\",\n      \"journal\": \"Biomedicine & Pharmacotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis mapping of interaction residues plus in vitro and in vivo functional validation, single lab\",\n      \"pmids\": [\"39913969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In TNBC, MLK4 mediates macrophage-induced cancer cell proliferation, ECM remodeling, migration, and invasion through activation of NF-κB and downstream matrix metalloproteinase (MMP) expression; MLK4-dependent paracrine signaling prominently upregulates CXCL1 and IL-8 in TNBC–macrophage co-culture.\",\n      \"method\": \"TNBC–macrophage co-culture system, MLK4 depletion, NF-κB activity assays, MMP expression profiling, migration/invasion assays\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function in co-culture model with defined molecular pathway readout, single lab\",\n      \"pmids\": [\"41922320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MLK4 knockdown in HCC cells elevated reactive oxygen species (ROS) production and increased phosphorylation of p38, JNK, and ERK1/2; blocking ROS generation or MAPKs signaling rescued the apoptosis and anti-metastatic effects caused by MLK4 silencing, placing MLK4 upstream of ROS/MAPKs in HCC.\",\n      \"method\": \"MLK4 siRNA knockdown, ROS measurement, Western blot for phospho-p38/JNK/ERK, pharmacological rescue with ROS scavengers and MAPK inhibitors, xenograft and metastasis models\",\n      \"journal\": \"Biomedicine & Pharmacotherapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — indirect upstream placement via pharmacological rescue, single lab, single method type\",\n      \"pmids\": [\"31071576\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAP3K21/MLK4 is a serine/threonine kinase that functions as an upstream MAP3K: it directly phosphorylates IKKα to activate NF-κB signaling, phosphorylates MEK1 to activate ERK, phosphorylates CREB to drive transcriptional targets including PCK1, and activates the JNK pathway; loss-of-function mutations in colon cancer suppress JNK signaling and reduce tumor-suppressive outputs, while gain-of-function in glioma and breast cancer drives NF-κB-dependent mesenchymal identity, DNA damage resistance, and invasiveness; MLK4 also interacts with TLR4 to negatively regulate LPS-induced JNK/ERK activation and TNF production, and its kinase domain engages IL-17RB through a defined R216–C408 interface to mediate oncogenic signaling in pancreatic cancer.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAP3K21 (MLK4) is a serine/threonine MAP3K-family kinase that integrates upstream signals into NF-\\u03baB, MAPK, and CREB transcriptional outputs to control cancer cell identity, survival, and invasion [#0, #2, #6]. Its best-defined biochemical activity is direct substrate phosphorylation: MLK4 binds and phosphorylates IKK\\u03b1 to activate NF-\\u03baB signaling that drives mesenchymal identity, self-renewal, motility, and radioresistance in glioma stem cells [#0], and phosphorylates MEK1 to engage the MEK/ERK axis, with MLK4-mutant alleles acting as constitutively active drivers that cooperate with activated RAS in colorectal cancer [#2]. MLK4 also phosphorylates the transcription factor CREB to induce PCK1 and reprogram glycolytic metabolism, with its own expression positively controlled by KLF5 [#6]. The kinase exerts context-dependent and opposing effects on the JNK pathway: loss-of-function mutations in colon cancer suppress JNK signaling, and restoring MLK4 activity reactivates JNK targets cJUN, ATF3, CDKN1A, and CDKN2B to limit tumor growth, a behavior rationalized by a catalytic-domain crystal structure explaining mutant inactivity [#1]. In breast cancer, MLK4 activates NF-\\u03baB to promote mesenchymal, migratory, and invasive phenotypes [#5], supports the DNA damage response through ATM/CHK2 phosphorylation and NHEJ-mediated repair [#4], and mediates macrophage-induced proliferation and ECM remodeling via NF-\\u03baB-driven MMP, CXCL1, and IL-8 expression [#8]. Beyond its oncogenic kinase activities, MLK4 interacts with TLR4 to negatively regulate LPS-induced JNK/ERK activation and TNF-\\u03b1 production in macrophages [#3], and engages IL-17RB through a defined R216\\u2013C408 interface that supports pancreatic cancer growth and metastasis [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Established the first signaling partner and an unexpectedly negative regulatory role, distinguishing MLK4 from other MLK-family MAP3Ks that activate stress kinases.\",\n      \"evidence\": \"Co-IP of TLR4, plus knockdown/overexpression in macrophages with LPS-induced cytokine and MAPK readouts\",\n      \"pmids\": [\"21602844\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the direct substrate through which MLK4 dampens TLR4 signaling\", \"Whether kinase activity is required for the negative-regulatory effect was not resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified MEK1 as a direct MLK4 substrate and showed cancer-associated alleles are constitutively active, framing MLK4 as a RAS-cooperating oncogenic kinase.\",\n      \"evidence\": \"Direct MEK1 phosphorylation assay, MLK4 knockout cells, transformation and xenograft assays\",\n      \"pmids\": [\"23319808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not reconcile activating CRC alleles here with loss-of-function CRC alleles reported elsewhere\", \"Structural basis of constitutive activation not defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolved a context where MLK4 is tumor-suppressive via JNK, and provided a catalytic-domain structure explaining how mutations inactivate the kinase.\",\n      \"evidence\": \"Reconstitution of MLK4 activity in mutant CRC cells, kinase assays, catalytic-domain crystal structure, in vivo tumor growth\",\n      \"pmids\": [\"26637668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which upstream signals select JNK versus MEK/ERK or NF-\\u03baB output\", \"Mechanistic basis for opposite mutational consequences across cancers unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defined the IKK\\u03b1\\u2013NF-\\u03baB axis as the route by which MLK4 enforces mesenchymal identity and radioresistance in glioma stem cells.\",\n      \"evidence\": \"Reciprocal Co-IP, direct IKK\\u03b1 phosphorylation assay, MLK4 silencing with mesenchymal-signature phenotypic readout\",\n      \"pmids\": [\"26859459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream activators recruiting MLK4 to IKK\\u03b1 not identified\", \"Selectivity for IKK\\u03b1 over other IKK subunits not addressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extended the NF-\\u03baB-driven mesenchymal program from glioma to breast cancer invasion.\",\n      \"evidence\": \"MLK4 silencing, NF-\\u03baB reporter, migration/invasion and 3D spheroid assays, xenograft\",\n      \"pmids\": [\"30552384\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct substrate in breast cancer NF-\\u03baB activation not confirmed\", \"Downstream effector genes not enumerated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Placed MLK4 upstream of a ROS/MAPK survival axis in hepatocellular carcinoma, with MLK4 loss promoting apoptosis.\",\n      \"evidence\": \"siRNA knockdown, ROS measurement, phospho-MAPK blots, pharmacological rescue, xenograft/metastasis models\",\n      \"pmids\": [\"31071576\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Upstream placement is indirect, inferred from pharmacological rescue rather than direct biochemistry\", \"No direct MLK4 substrate identified in this pathway\", \"Single method type, not independently confirmed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected MLK4 to genome maintenance, showing it promotes ATM/CHK2-mediated DNA damage response and NHEJ repair to support survival in TNBC.\",\n      \"evidence\": \"MLK4 knockdown/inhibition, phosphoproteomics, NF-\\u03baB reporter, mRNA-seq, in vivo doxorubicin sensitivity\",\n      \"pmids\": [\"34839359\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MLK4 directly phosphorylates ATM/CHK2 or acts indirectly not resolved\", \"Mechanistic link between NF-\\u03baB cytokine output and repair not dissected\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Added a metabolic output by showing MLK4 phosphorylates CREB to drive PCK1 and glycolytic reprogramming, and identified KLF5 as a transcriptional activator of MLK4.\",\n      \"evidence\": \"CREB phosphorylation assay, promoter/reporter analysis, metabolomic profiling, knockdown\",\n      \"pmids\": [\"37407566\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CREB phosphorylation is direct versus relayed not fully established\", \"Generality of the CREB\\u2013PCK1 axis beyond lung adenocarcinoma untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mapped a druggable IL-17RB\\u2013MLK4 interface (IL-17RB C408 / MLK4 R216), establishing a protein-protein interaction route to oncogenic signaling in pancreatic cancer.\",\n      \"evidence\": \"Site-directed mutagenesis of interface residues, cyclic-peptide disruption, in vitro and orthotopic in vivo growth/metastasis assays\",\n      \"pmids\": [\"39913969\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream signaling triggered by the IL-17RB\\u2013MLK4 interaction not delineated\", \"Whether the interaction modulates MLK4 catalytic activity unknown\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Showed MLK4 mediates tumor\\u2013macrophage crosstalk, driving NF-\\u03baB-dependent MMP, CXCL1, and IL-8 to promote ECM remodeling and invasion in TNBC.\",\n      \"evidence\": \"TNBC\\u2013macrophage co-culture, MLK4 depletion, NF-\\u03baB assays, MMP profiling, migration/invasion assays\",\n      \"pmids\": [\"41922320\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct substrate linking macrophage cues to MLK4 activation not identified\", \"Receptor relaying macrophage signal to MLK4 not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how a single kinase produces opposing outputs\\u2014tumor-suppressive JNK activation versus oncogenic NF-\\u03baB/ERK signaling\\u2014and what upstream receptors and contextual cues dictate substrate selection.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model of context-dependent substrate choice\", \"Physiological (non-cancer) function and endogenous activators largely uncharacterized in the corpus\", \"Whether IL-17RB and TLR4 engagement converge on the same catalytic outputs unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 6]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 2, 6]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 2, 5, 7, 8]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CHUK\", \"MAP2K1\", \"TLR4\", \"IL17RB\", \"CREB1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}