{"gene":"MAPK4","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2006,"finding":"ERK4 (MAPK4) binds to endogenous MK5 (MAPKAP kinase 5), and this interaction leads to translocation of MK5 to the cytoplasm and activation of MK5 by phosphorylation. Unlike ERK3, ERK4 is a stable protein, and its catalytic activity is necessary for MK5 activation (catalytically dead ERK4 cannot activate MK5). ERK4 also dimerizes/oligomerizes with ERK3, suggesting cooperative activation of MK5.","method":"Co-immunoprecipitation, transfection of catalytically dead mutants in HEK293 cells, subcellular localization assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, catalytic dead mutant analysis, replicated independently by two labs in the same year (PMIDs 16973613 and 16971392)","pmids":["16973613"],"is_preprint":false},{"year":2006,"finding":"ERK4 (MAPK4) is a bona fide interaction partner of MK5. Binding of ERK4 to MK5 results in phosphorylation and activation of MK5 and relocalization of MK5 from nucleus to cytoplasm. Knockdown of ERK4 in HeLa cells reduces endogenous MK5 activity by ~50%; combined knockdown of ERK4 and ERK3 reduces MK5 activity by >80%, establishing both as physiological regulators of MK5.","method":"Co-immunoprecipitation, siRNA knockdown, subcellular localization assays, kinase activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, siRNA knockdown with quantified activity readout, replicated by independent lab (PMID 16973613)","pmids":["16971392"],"is_preprint":false},{"year":2008,"finding":"Ser186 within the SEG activation loop motif of ERK4 (MAPK4) is phosphorylated in vivo by an upstream kinase (not autophosphorylation). This phosphorylation is required for the interaction with MK5, for cytoplasmic anchoring of MK5, and for activation of MK5. Alanine or glutamate substitution at Ser186 abrogates ERK4-MK5 complex formation and MK5 activation. Co-expression of MK5 increases Ser186 phosphorylation, suggesting MK5 binding facilitates ERK4 phosphorylation.","method":"In vivo phosphorylation assays, kinase-dead and phospho-mutant ERK4 constructs, Co-immunoprecipitation, subcellular localization assays, SDS-PAGE mobility shift analysis","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — site-directed mutagenesis of activation loop residue combined with Co-IP and functional activation assays in single lab with multiple orthogonal methods","pmids":["18248330"],"is_preprint":false},{"year":2008,"finding":"Activation loop phosphorylation of ERK4 (MAPK4) at Ser186 (SEG motif) is detected in resting cells and is not further stimulated by mitogenic or stress stimuli. This phosphorylation stimulates intrinsic catalytic activity of ERK4 and is required for formation of stable active complexes with MK5 and for cytoplasmic redistribution of ERK4-MK5 complexes. Phosphorylation is exerted in trans by an upstream cellular kinase.","method":"In vivo phosphorylation, pharmacological and mutant analyses, kinase activity assays, co-immunoprecipitation, subcellular fractionation","journal":"Journal of cellular physiology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — activation loop mutagenesis with catalytic and complex-formation readouts, multiple orthogonal methods in single study","pmids":["18720373"],"is_preprint":false},{"year":2009,"finding":"ERK4 (MAPK4) interacts with MK5 via a novel interaction motif 'FRIEDE' located in the L16 extension C-terminal to the CD domain. The canonical CD domain is dispensable for ERK3/4-MK5 interaction. A single isoleucine-to-lysine substitution in FRIEDE abolishes binding, activation, and translocation of MK5 by ERK4. Activation loop phosphorylation gates accessibility of the FRIEDE motif, suggesting a phosphorylation-dependent switch mechanism.","method":"Peptide overlay assays, site-directed mutagenesis of FRIEDE motif, Co-immunoprecipitation, subcellular localization assays, kinase activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis of interaction motif combined with binding, activation, and localization readouts; multiple orthogonal methods in single study","pmids":["19473979"],"is_preprint":false},{"year":2010,"finding":"Group I p21-activated kinases (PAK1, PAK2, PAK3) phosphorylate ERK4 (MAPK4) on its activation loop residue Ser186 both in vitro and in vivo, thereby activating ERK4. Expression of activated Rac1 augments this phosphorylation; siRNA silencing of PAK1/2/3 abolishes Rac1-induced ERK4 Ser186 phosphorylation. PAK-mediated phosphorylation of ERK4 results in downstream activation of MK5, defining a PAK-ERK4-MK5 signaling pathway.","method":"Biochemical kinase purification, in vitro kinase assays, siRNA knockdown, expression of activated Rac1, in vivo phosphorylation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with purified components plus in vivo RNAi validation; multiple orthogonal approaches in single study","pmids":["21177870"],"is_preprint":false},{"year":2010,"finding":"Mapk4-knockout mice are viable and fertile with no gross morphological or physiological anomalies. Loss of Erk4 does not alter Erk3 expression or activity and does not exacerbate Erk3-null phenotypes (fetal growth restriction, pulmonary immaturity). However, Erk4-deficient mice display depression-like behavior in the forced-swimming test, indicating a specific non-redundant behavioral function.","method":"Targeted gene disruption in mice (Mapk4 knockout), developmental and physiological phenotyping, behavioral tests (forced-swimming), western blotting","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic knockout with defined physiological and behavioral phenotypes, multiple characterization methods in single study","pmids":["20956558"],"is_preprint":false},{"year":2017,"finding":"The dual-specificity phosphatase DUSP2 binds directly to ERK4 (MAPK4) via interaction between the DUSP2 kinase interaction motif (KIM) and the conserved CD domain of ERK4. This interaction results in dephosphorylation of ERK4's activation loop and stabilization of DUSP2. ERK4 kinase activity is required for DUSP2 stabilization. DUSP2 expression inhibits ERK4-mediated activation of MK5.","method":"Co-immunoprecipitation, direct binding assays, phosphorylation assays, DUSP2 stability measurements, kinase-dead ERK4 mutants, MK5 activity assays","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct binding confirmed, mutagenesis of interaction domains, multiple functional readouts (dephosphorylation, stabilization, MK5 activity) in single study","pmids":["28252035"],"is_preprint":false},{"year":2019,"finding":"MAPK4 directly binds and phosphorylates AKT at threonine 308 (activation loop) independent of PI3K. MAPK4 also activates mTORC2 to phosphorylate AKT at serine 473, enabling full AKT activation. This non-canonical AKT activation promotes oncogenic outcomes including anchorage-independent growth. MAPK4 overexpression transforms prostate epithelial cells; MAPK4 knockdown inhibits cancer cell proliferation and xenograft growth.","method":"Co-immunoprecipitation, in vitro kinase assays, phospho-specific western blotting, site-directed mutagenesis, xenograft tumor models, TCGA correlation analysis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct kinase assay showing MAPK4 phosphorylates AKT T308, replicated in cancer contexts, multiple orthogonal methods","pmids":["30688659"],"is_preprint":false},{"year":2021,"finding":"MAPK4 activates the androgen receptor (AR) by enhancing GATA2 transcriptional expression and stabilizing GATA2 protein through repression of GATA2 ubiquitination and degradation. Concerted activation of both GATA2/AR and AKT pathways by MAPK4 promotes prostate cancer cell proliferation, anchorage-independent growth, xenograft growth, and castration resistance. Both pathways are necessary for MAPK4 tumor-promoting activity.","method":"Western blotting, ubiquitination assays, gene knockdown and overexpression, xenograft mouse models, CRPC patient sample correlation","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (ubiquitination assay, xenograft, patient correlation), replicated MAPK4-AKT axis from prior study, new GATA2/AR mechanism established","pmids":["33586682"],"is_preprint":false},{"year":2022,"finding":"MAPK4 drives AKT activation independent of PI3K in a large subset of triple-negative breast cancer (TNBC) cells. MAPK4 expression is critical for TNBC cell and xenograft growth. Repressing MAPK4 sensitizes TNBC cells and xenografts to PI3K inhibitors by removing a PI3K-bypass mechanism for AKT activation.","method":"siRNA/shRNA knockdown, AKT phosphorylation assays, PI3K inhibitor drug sensitivity assays, xenograft mouse models","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — xenograft models plus biochemical AKT activation assays and drug synergy experiments; consistent with established MAPK4-AKT mechanism","pmids":["35017531"],"is_preprint":false},{"year":2023,"finding":"MAPK4 also enhances PDK1 protein synthesis, thereby phosphorylating/activating PDK1 substrates beyond AKT. This MAPK4-PDK1 axis cooperates with the MAPK4-AKT axis to promote tumor growth and confer resistance to both PI3K and PI3K/PDK1 co-blockade in TNBC cells.","method":"Protein synthesis assays, PDK1 substrate phosphorylation assays, siRNA knockdown, drug resistance assays in TNBC cell models","journal":"PLoS biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — new mechanistic axis (MAPK4-PDK1) supported by biochemical and cell-based data, single lab, consistent with established MAPK4 biology","pmids":["37531320"],"is_preprint":false},{"year":2023,"finding":"MAPK4 depletion in gastric cancer cells induces secretion of macrophage migration inhibitory factor (MIF), which polarizes tumor-associated macrophages (TAMs). In turn, TAMs activate epithelial-mesenchymal transition in gastric cancer cells and suppress MAPK4 expression, creating a positive feedback loop that facilitates liver metastasis in orthotopic mouse models.","method":"In vivo orthotopic mouse models, shRNA knockdown, cytokine measurement (MIF secretion), transcriptome profiling, tissue array analysis","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo orthotopic model with mechanistic feedback loop identified, single lab, multiple methods","pmids":["36797541"],"is_preprint":false},{"year":2020,"finding":"MAPK4 knockout reduces AKT phosphorylation in cervical cancer cells, impairing DNA repair signaling (reduced p-DNA-PK and RAD51), which enhances radiation sensitivity and sensitivity to PARP1 inhibitors. Constitutively active AKT rescues DNA repair protein expression in MAPK4 KO cells, placing MAPK4 upstream of AKT in this DNA repair context.","method":"CRISPR knockout, western blotting, colony formation assay, immunofluorescence, xenograft mouse models, constitutively active AKT rescue experiments","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with AKT rescue experiment establishing pathway placement, supported by in vivo xenograft data, single lab","pmids":["32711558"],"is_preprint":false},{"year":2020,"finding":"MAPK4 deficiency in mice reduces signaling through MK5, AKT, JNK, and p38 MAPK pathways in LPS-induced acute lung injury. MAPK4 KO mice show prolonged survival, reduced pro-inflammatory cytokines, and altered immune cell composition in bronchoalveolar lavage fluid. MAPK4 expression in macrophages is upregulated by LPS, and MAPK4 knockdown reduces pro-inflammatory cytokine expression in macrophages.","method":"MAPK4 knockout mice, LPS-induced ALI model, shRNA knockdown in macrophages, signaling pathway analysis by western blot, cytokine measurement","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout with in vivo phenotype and defined signaling readouts, single lab","pmids":["33088477"],"is_preprint":false},{"year":2024,"finding":"MAPK4 silencing in endothelial cells inhibits their proliferation and migration, and increases ERK1/2 pathway signaling (but not AKT or JNK). In vivo, targeted silencing of MAPK4 in endothelial cells using CD34 promoter-driven siRNA inhibits tumor angiogenesis and NSCLC growth, indicating MAPK4 facilitates angiogenesis partly by suppressing ERK1/2 signaling in endothelial cells.","method":"siRNA knockdown, flow cytometry, immunofluorescence, whole-genome transcriptional analysis, western blotting, in vivo tumor model with CD34 promoter-driven siRNA","journal":"Cancer innovation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo model with endothelial-cell-specific knockdown and defined ERK1/2 pathway readout, single lab","pmids":["38947754"],"is_preprint":false},{"year":2024,"finding":"MAPK4 translocates to the nucleus in response to MC-LR exposure and binds to the GATA2 protein (residues 295-480), enhancing SNCA gene transcription and thereby increasing α-synuclein protein expression, contributing to Lewy body formation and Parkinson's-like pathology.","method":"Nuclear fractionation, co-immunoprecipitation of MAPK4 and GATA2, luciferase reporter assay for SNCA transcription, western blotting, in vitro and in vivo MC-LR exposure models","journal":"Molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — nuclear translocation plus direct GATA2 binding and SNCA transcription readout; single lab with multiple methods","pmids":["39738876"],"is_preprint":false},{"year":2025,"finding":"MAPK4 inhibits PI3K-AKT-mTOR signaling in B cells by activating the IRF4-SHIP1 pathway. MAPK4 KO mice show enhanced proximal BCR signaling, heightened B cell proliferation, higher IL-6 production, and impaired marginal zone B cell differentiation. The MAPK4 agonist Vacquinol-1 enhances MZ B cell differentiation and reduces IL-6 secretion in collagen-induced arthritis models.","method":"MAPK4 knockout mice, pharmacological agonist (Vacquinol-1), flow cytometry, cytokine measurement, signaling pathway analysis by western blotting, collagen-induced arthritis model","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined signaling pathway placement (IRF4-SHIP1 downstream of MAPK4), multiple readouts, single lab","pmids":["39863600"],"is_preprint":false},{"year":2024,"finding":"FUS RNA binding protein stabilizes MAPK4 mRNA in TNBC cells, as shown by RNA immunoprecipitation. Puerarin treatment downregulates both FUS and MAPK4, and MAPK4 overexpression attenuates puerarin's anti-tumor effects, placing FUS upstream of MAPK4 in this regulatory axis.","method":"RNA immunoprecipitation (RIP) assay, western blotting, qRT-PCR, overexpression rescue experiments, xenograft mouse model","journal":"Chemical biology & drug design","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — RIP assay establishes FUS-MAPK4 mRNA interaction, rescue experiment supports pathway placement, single lab","pmids":["39223105"],"is_preprint":false},{"year":2025,"finding":"A spermidine derivative (SPDD) weakens the interaction between MAPK4 and AKT, resulting in decreased AKT phosphorylation and reduced expression of IL-6, IL-1β, iNOS, and COX-2, thereby alleviating colitis. This places MAPK4 as a direct physical mediator of AKT activation in the inflammatory context.","method":"Co-immunoprecipitation (MAPK4-AKT interaction assay), RNA-seq, western blotting, DSS-induced colitis mouse model, Caco-2 cell inflammation model","journal":"Foods (Basel, Switzerland)","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP assay in a pharmacological study; consistent with established MAPK4-AKT mechanism but single lab, single method for the mechanistic claim","pmids":["40238233"],"is_preprint":false}],"current_model":"MAPK4 (ERK4) is an atypical MAPK that is constitutively phosphorylated at its activation loop Ser186 by group I PAKs downstream of Rac1; phospho-Ser186 enables MAPK4 to bind MK5 via a novel FRIEDE docking motif, translocate MK5 to the cytoplasm, and directly phosphorylate/activate MK5, while DUSP2 dephosphorylates and inactivates this pathway. Beyond the MK5 axis, MAPK4 can non-canonically activate AKT by directly phosphorylating its T308 activation loop and by engaging mTORC2 for S473 phosphorylation independent of PI3K, and also enhances PDK1 protein synthesis, thereby cooperatively driving oncogenic AKT/mTOR signaling, AR activation via GATA2 stabilization, tumor angiogenesis, and inflammatory responses in multiple cancer and disease contexts."},"narrative":{"mechanistic_narrative":"MAPK4 (ERK4) is an atypical, constitutively active MAP kinase that functions as a stable upstream activator of MK5 and, in disease contexts, as a non-canonical driver of oncogenic AKT signaling [PMID:16971392, PMID:30688659]. Its activation loop residue Ser186 within the SEG motif is phosphorylated in trans by an upstream kinase in resting cells rather than by autophosphorylation, and this phosphorylation stimulates intrinsic catalytic activity and gates the protein's signaling output [PMID:18248330, PMID:18720373]; group I PAKs (PAK1/2/3) acting downstream of Rac1 are the responsible kinases [PMID:21177870]. Phospho-Ser186 enables MAPK4 to bind MK5 through a non-canonical FRIEDE docking motif in the L16 extension, anchoring MK5 in the cytoplasm and directly phosphorylating and activating it, while ERK3 dimerization cooperatively reinforces MK5 activation [PMID:16973613, PMID:19473979]. The dual-specificity phosphatase DUSP2 docks on the MAPK4 CD domain and dephosphorylates the activation loop, switching off the pathway [PMID:28252035]. Separately, MAPK4 directly binds and phosphorylates AKT at Thr308 independent of PI3K and engages mTORC2 for Ser473 phosphorylation, and additionally enhances PDK1 protein synthesis, together driving anchorage-independent growth, tumor xenograft growth, and resistance to PI3K-pathway inhibitors across prostate and triple-negative breast cancers [PMID:30688659, PMID:35017531, PMID:37531320]. In prostate cancer this AKT axis cooperates with MAPK4-mediated stabilization of GATA2 and androgen receptor activation to promote castration resistance [PMID:33586682]. Genetic loss of Mapk4 in mice is compatible with viability and fertility but produces a depression-like behavioral phenotype, and Mapk4 also shapes inflammatory and angiogenic responses in multiple tissue contexts [PMID:20956558].","teleology":[{"year":2006,"claim":"Established that the orphan atypical kinase ERK4 has a defined substrate by identifying MK5 as its binding partner and demonstrating catalysis-dependent activation, answering what ERK4 actually does.","evidence":"Reciprocal Co-IP, catalytically dead mutants, and siRNA knockdown with kinase activity readouts in HEK293/HeLa cells, replicated by two independent labs","pmids":["16973613","16971392"],"confidence":"High","gaps":["The upstream kinase activating ERK4 was unknown","Structural basis of the ERK4-MK5 interaction not yet defined"]},{"year":2008,"claim":"Resolved how ERK4 is regulated by showing that activation-loop Ser186 is phosphorylated in trans in resting cells and is required for MK5 binding, cytoplasmic anchoring, and activation.","evidence":"In vivo phosphorylation assays, phospho-mutant constructs, mobility-shift, Co-IP and localization assays across two studies","pmids":["18248330","18720373"],"confidence":"High","gaps":["Identity of the upstream Ser186 kinase unresolved","Why phosphorylation is constitutive rather than stimulus-induced not explained"]},{"year":2009,"claim":"Defined the molecular docking mechanism by identifying the non-canonical FRIEDE motif, not the canonical CD domain, as the MK5-binding interface gated by activation-loop phosphorylation.","evidence":"Peptide overlay assays, FRIEDE point mutagenesis, Co-IP, localization, and kinase activity assays","pmids":["19473979"],"confidence":"High","gaps":["No structural model of the phospho-gated FRIEDE switch","Whether other partners use this docking site untested"]},{"year":2010,"claim":"Identified the long-sought upstream kinase, placing ERK4 in a Rac1-PAK-ERK4-MK5 signaling cascade.","evidence":"Biochemical kinase purification, in vitro kinase assays, siRNA of PAK1/2/3, and activated Rac1 expression","pmids":["21177870"],"confidence":"High","gaps":["Physiological stimuli engaging Rac1-PAK to control ERK4 not mapped","Tissue contexts where this cascade operates unknown"]},{"year":2010,"claim":"Defined the organismal role of Mapk4 through knockout, revealing a non-redundant behavioral function distinct from Erk3.","evidence":"Targeted Mapk4 disruption in mice with developmental, physiological, and forced-swim behavioral phenotyping","pmids":["20956558"],"confidence":"High","gaps":["Molecular basis of the depression-like phenotype unexplained","Whether the MK5 axis underlies the behavioral effect untested"]},{"year":2017,"claim":"Identified the off-switch of the pathway by showing DUSP2 dephosphorylates the ERK4 activation loop via CD-domain docking, with reciprocal stabilization of DUSP2.","evidence":"Co-IP, direct binding, dephosphorylation assays, DUSP2 stability measurements, and MK5 activity readouts","pmids":["28252035"],"confidence":"High","gaps":["Physiological signals controlling DUSP2-ERK4 engagement unknown","Whether DUSP2 regulates the AKT branch untested"]},{"year":2019,"claim":"Revealed a non-canonical oncogenic function by showing MAPK4 directly phosphorylates AKT T308 independent of PI3K and engages mTORC2 for S473, transforming cells.","evidence":"Co-IP, in vitro kinase assays, phospho-specific blotting, mutagenesis, xenografts, and TCGA correlation","pmids":["30688659"],"confidence":"High","gaps":["How MAPK4 recruits/activates mTORC2 mechanistically unresolved","Relationship between the MK5 and AKT branches unclear"]},{"year":2020,"claim":"Extended the MAPK4-AKT axis to therapeutic vulnerabilities, placing MAPK4 upstream of AKT-dependent DNA repair and inflammatory/radiation responses.","evidence":"CRISPR KO with constitutively active AKT rescue in cervical cancer; knockout mice in LPS-induced acute lung injury with multi-pathway signaling readouts","pmids":["32711558","33088477"],"confidence":"Medium","gaps":["Direct versus indirect control of DNA repair factors not separated","Tissue-specific kinase substrates beyond AKT undefined"]},{"year":2021,"claim":"Established a second oncogenic branch in prostate cancer, showing MAPK4 stabilizes GATA2 and activates AR cooperatively with AKT to drive castration resistance.","evidence":"Ubiquitination assays, knockdown/overexpression, xenografts, and CRPC patient correlation","pmids":["33586682"],"confidence":"High","gaps":["Mechanism by which MAPK4 represses GATA2 ubiquitination unknown","Whether GATA2 stabilization is kinase-dependent untested"]},{"year":2022,"claim":"Generalized MAPK4 as a PI3K-bypass mechanism, demonstrating that its depletion sensitizes TNBC to PI3K inhibitors.","evidence":"siRNA/shRNA knockdown, AKT phosphorylation assays, PI3K inhibitor sensitivity, and xenografts","pmids":["35017531"],"confidence":"High","gaps":["Predictive biomarkers for MAPK4-driven PI3K resistance undefined","Combination dosing strategies not optimized"]},{"year":2023,"claim":"Broadened MAPK4 oncogenic output beyond AKT by linking it to PDK1 protein synthesis and to a macrophage-driven metastatic feedback loop.","evidence":"Protein synthesis and PDK1 substrate assays with drug resistance studies in TNBC; orthotopic gastric cancer models with MIF/TAM profiling","pmids":["37531320","36797541"],"confidence":"Medium","gaps":["How MAPK4 enhances PDK1 translation mechanistically unknown","The MIF-TAM feedback effectors downstream of MAPK4 not fully defined"]},{"year":2024,"claim":"Documented context-specific and nuclear functions of MAPK4 in angiogenesis and neurodegeneration, expanding its roles beyond cancer cell-intrinsic AKT signaling.","evidence":"Endothelial-specific CD34-driven siRNA in NSCLC tumor models with ERK1/2 readouts; nuclear fractionation, MAPK4-GATA2 Co-IP and SNCA reporter assays in MC-LR exposure models","pmids":["38947754","39738876"],"confidence":"Medium","gaps":["How MAPK4 suppresses endothelial ERK1/2 mechanistically unknown","Trigger and regulation of MAPK4 nuclear translocation undefined"]},{"year":2025,"claim":"Revealed immunoregulatory and pharmacologically tractable roles, with MAPK4 restraining BCR/PI3K signaling via IRF4-SHIP1 and serving as a druggable AKT-interaction node in inflammation.","evidence":"Knockout mice with Vacquinol-1 agonist in arthritis models; Co-IP disruption by spermidine derivative in colitis models","pmids":["39863600","40238233"],"confidence":"Medium","gaps":["Reconciliation of MAPK4 inhibiting versus activating AKT across cell types unresolved","The colitis MAPK4-AKT claim rests on a single Co-IP method"]},{"year":null,"claim":"How MAPK4 switches between its MK5 axis and its AKT/PDK1/GATA2 axes, and what determines its opposing effects on AKT in different cell types, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the MAPK4-AKT or MAPK4-mTORC2 interaction","Determinants of context-dependent positive versus negative regulation of PI3K-AKT undefined","Whether the constitutive Rac1-PAK input controls the oncogenic branches untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,8]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,5,8]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[9,16]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,1,3]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[16]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,8]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8,9,10]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[14,17]}],"complexes":[],"partners":["MK5","DUSP2","AKT1","GATA2","PAK1","ERK3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P31152","full_name":"Mitogen-activated protein kinase 4","aliases":["Extracellular signal-regulated kinase 4","ERK-4","MAP kinase isoform p63","p63-MAPK"],"length_aa":587,"mass_kda":65.9,"function":"Atypical MAPK protein. Phosphorylates microtubule-associated protein 2 (MAP2) and MAPKAPK5. The precise role of the complex formed with MAPKAPK5 is still unclear, but the complex follows a complex set of phosphorylation events: upon interaction with atypical MAPKAPK5, ERK4/MAPK4 is phosphorylated at Ser-186 and then mediates phosphorylation and activation of MAPKAPK5, which in turn phosphorylates ERK4/MAPK4. May promote entry in the cell cycle (By similarity)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P31152/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MAPK4","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MAPK4","total_profiled":1310},"omim":[{"mim_id":"602904","title":"MITOGEN-ACTIVATED PROTEIN KINASE 6; MAPK6","url":"https://www.omim.org/entry/602904"},{"mim_id":"176949","title":"MITOGEN-ACTIVATED PROTEIN KINASE 4; MAPK4","url":"https://www.omim.org/entry/176949"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Midbody","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":72.2},{"tissue":"parathyroid gland","ntpm":47.9}],"url":"https://www.proteinatlas.org/search/MAPK4"},"hgnc":{"alias_symbol":["Erk3-related","Erk4"],"prev_symbol":["PRKM4"]},"alphafold":{"accession":"P31152","domains":[{"cath_id":"3.30.200.20","chopping":"17-107","consensus_level":"high","plddt":86.3237,"start":17,"end":107},{"cath_id":"1.10.510.10","chopping":"111-328","consensus_level":"high","plddt":88.3426,"start":111,"end":328}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P31152","model_url":"https://alphafold.ebi.ac.uk/files/AF-P31152-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P31152-F1-predicted_aligned_error_v6.png","plddt_mean":63.53},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MAPK4","jax_strain_url":"https://www.jax.org/strain/search?query=MAPK4"},"sequence":{"accession":"P31152","fasta_url":"https://rest.uniprot.org/uniprotkb/P31152.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P31152/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P31152"}},"corpus_meta":[{"pmid":"31992303","id":"PMC_31992303","title":"Circular RNA MAPK4 (circ-MAPK4) inhibits cell apoptosis via MAPK signaling pathway by sponging miR-125a-3p in gliomas.","date":"2020","source":"Molecular cancer","url":"https://pubmed.ncbi.nlm.nih.gov/31992303","citation_count":115,"is_preprint":false},{"pmid":"30728056","id":"PMC_30728056","title":"CircRNA circ_0000190 inhibits the progression of multiple myeloma through modulating miR-767-5p/MAPK4 pathway.","date":"2019","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/30728056","citation_count":107,"is_preprint":false},{"pmid":"30688659","id":"PMC_30688659","title":"MAPK4 overexpression promotes tumor progression via noncanonical activation of AKT/mTOR signaling.","date":"2019","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/30688659","citation_count":77,"is_preprint":false},{"pmid":"16973613","id":"PMC_16973613","title":"Characterization of the atypical MAPK ERK4 and its activation of the MAPK-activated protein kinase MK5.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16973613","citation_count":74,"is_preprint":false},{"pmid":"16971392","id":"PMC_16971392","title":"Regulation of MAPK-activated protein kinase 5 activity and subcellular localization by the atypical MAPK ERK4/MAPK4.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16971392","citation_count":64,"is_preprint":false},{"pmid":"18720373","id":"PMC_18720373","title":"Activation loop phosphorylation of the atypical MAP kinases ERK3 and ERK4 is required for binding, activation and cytoplasmic relocalization of MK5.","date":"2008","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/18720373","citation_count":64,"is_preprint":false},{"pmid":"21177870","id":"PMC_21177870","title":"Activation loop phosphorylation of ERK3/ERK4 by group I p21-activated kinases (PAKs) defines a novel PAK-ERK3/4-MAPK-activated protein kinase 5 signaling pathway.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21177870","citation_count":58,"is_preprint":false},{"pmid":"33586682","id":"PMC_33586682","title":"MAPK4 promotes prostate cancer by concerted activation of androgen receptor and AKT.","date":"2021","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/33586682","citation_count":46,"is_preprint":false},{"pmid":"25359475","id":"PMC_25359475","title":"Linear B-cell epitope mapping of MAPK3 and MAPK4 from Leishmania braziliensis: implications for the serodiagnosis of human and canine leishmaniasis.","date":"2014","source":"Applied microbiology and biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/25359475","citation_count":40,"is_preprint":false},{"pmid":"35017531","id":"PMC_35017531","title":"MAPK4 promotes triple negative breast cancer growth and reduces tumor sensitivity to PI3K 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Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/40238233","citation_count":1,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.10.23.682825","title":"Systemic infections alter cortical transcriptionalsignatures in Alzheimer’s disease","date":"2025-10-24","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.23.682825","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":22283,"output_tokens":5603,"usd":0.075447,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14097,"output_tokens":4339,"usd":0.08948,"stage2_stop_reason":"end_turn"},"total_usd":0.164927,"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\": 2006,\n      \"finding\": \"ERK4 (MAPK4) binds to endogenous MK5 (MAPKAP kinase 5), and this interaction leads to translocation of MK5 to the cytoplasm and activation of MK5 by phosphorylation. Unlike ERK3, ERK4 is a stable protein, and its catalytic activity is necessary for MK5 activation (catalytically dead ERK4 cannot activate MK5). ERK4 also dimerizes/oligomerizes with ERK3, suggesting cooperative activation of MK5.\",\n      \"method\": \"Co-immunoprecipitation, transfection of catalytically dead mutants in HEK293 cells, subcellular localization assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, catalytic dead mutant analysis, replicated independently by two labs in the same year (PMIDs 16973613 and 16971392)\",\n      \"pmids\": [\"16973613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ERK4 (MAPK4) is a bona fide interaction partner of MK5. Binding of ERK4 to MK5 results in phosphorylation and activation of MK5 and relocalization of MK5 from nucleus to cytoplasm. Knockdown of ERK4 in HeLa cells reduces endogenous MK5 activity by ~50%; combined knockdown of ERK4 and ERK3 reduces MK5 activity by >80%, establishing both as physiological regulators of MK5.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, subcellular localization assays, kinase activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, siRNA knockdown with quantified activity readout, replicated by independent lab (PMID 16973613)\",\n      \"pmids\": [\"16971392\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Ser186 within the SEG activation loop motif of ERK4 (MAPK4) is phosphorylated in vivo by an upstream kinase (not autophosphorylation). This phosphorylation is required for the interaction with MK5, for cytoplasmic anchoring of MK5, and for activation of MK5. Alanine or glutamate substitution at Ser186 abrogates ERK4-MK5 complex formation and MK5 activation. Co-expression of MK5 increases Ser186 phosphorylation, suggesting MK5 binding facilitates ERK4 phosphorylation.\",\n      \"method\": \"In vivo phosphorylation assays, kinase-dead and phospho-mutant ERK4 constructs, Co-immunoprecipitation, subcellular localization assays, SDS-PAGE mobility shift analysis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — site-directed mutagenesis of activation loop residue combined with Co-IP and functional activation assays in single lab with multiple orthogonal methods\",\n      \"pmids\": [\"18248330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Activation loop phosphorylation of ERK4 (MAPK4) at Ser186 (SEG motif) is detected in resting cells and is not further stimulated by mitogenic or stress stimuli. This phosphorylation stimulates intrinsic catalytic activity of ERK4 and is required for formation of stable active complexes with MK5 and for cytoplasmic redistribution of ERK4-MK5 complexes. Phosphorylation is exerted in trans by an upstream cellular kinase.\",\n      \"method\": \"In vivo phosphorylation, pharmacological and mutant analyses, kinase activity assays, co-immunoprecipitation, subcellular fractionation\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — activation loop mutagenesis with catalytic and complex-formation readouts, multiple orthogonal methods in single study\",\n      \"pmids\": [\"18720373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ERK4 (MAPK4) interacts with MK5 via a novel interaction motif 'FRIEDE' located in the L16 extension C-terminal to the CD domain. The canonical CD domain is dispensable for ERK3/4-MK5 interaction. A single isoleucine-to-lysine substitution in FRIEDE abolishes binding, activation, and translocation of MK5 by ERK4. Activation loop phosphorylation gates accessibility of the FRIEDE motif, suggesting a phosphorylation-dependent switch mechanism.\",\n      \"method\": \"Peptide overlay assays, site-directed mutagenesis of FRIEDE motif, Co-immunoprecipitation, subcellular localization assays, kinase activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis of interaction motif combined with binding, activation, and localization readouts; multiple orthogonal methods in single study\",\n      \"pmids\": [\"19473979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Group I p21-activated kinases (PAK1, PAK2, PAK3) phosphorylate ERK4 (MAPK4) on its activation loop residue Ser186 both in vitro and in vivo, thereby activating ERK4. Expression of activated Rac1 augments this phosphorylation; siRNA silencing of PAK1/2/3 abolishes Rac1-induced ERK4 Ser186 phosphorylation. PAK-mediated phosphorylation of ERK4 results in downstream activation of MK5, defining a PAK-ERK4-MK5 signaling pathway.\",\n      \"method\": \"Biochemical kinase purification, in vitro kinase assays, siRNA knockdown, expression of activated Rac1, in vivo phosphorylation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with purified components plus in vivo RNAi validation; multiple orthogonal approaches in single study\",\n      \"pmids\": [\"21177870\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Mapk4-knockout mice are viable and fertile with no gross morphological or physiological anomalies. Loss of Erk4 does not alter Erk3 expression or activity and does not exacerbate Erk3-null phenotypes (fetal growth restriction, pulmonary immaturity). However, Erk4-deficient mice display depression-like behavior in the forced-swimming test, indicating a specific non-redundant behavioral function.\",\n      \"method\": \"Targeted gene disruption in mice (Mapk4 knockout), developmental and physiological phenotyping, behavioral tests (forced-swimming), western blotting\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with defined physiological and behavioral phenotypes, multiple characterization methods in single study\",\n      \"pmids\": [\"20956558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The dual-specificity phosphatase DUSP2 binds directly to ERK4 (MAPK4) via interaction between the DUSP2 kinase interaction motif (KIM) and the conserved CD domain of ERK4. This interaction results in dephosphorylation of ERK4's activation loop and stabilization of DUSP2. ERK4 kinase activity is required for DUSP2 stabilization. DUSP2 expression inhibits ERK4-mediated activation of MK5.\",\n      \"method\": \"Co-immunoprecipitation, direct binding assays, phosphorylation assays, DUSP2 stability measurements, kinase-dead ERK4 mutants, MK5 activity assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding confirmed, mutagenesis of interaction domains, multiple functional readouts (dephosphorylation, stabilization, MK5 activity) in single study\",\n      \"pmids\": [\"28252035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MAPK4 directly binds and phosphorylates AKT at threonine 308 (activation loop) independent of PI3K. MAPK4 also activates mTORC2 to phosphorylate AKT at serine 473, enabling full AKT activation. This non-canonical AKT activation promotes oncogenic outcomes including anchorage-independent growth. MAPK4 overexpression transforms prostate epithelial cells; MAPK4 knockdown inhibits cancer cell proliferation and xenograft growth.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assays, phospho-specific western blotting, site-directed mutagenesis, xenograft tumor models, TCGA correlation analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct kinase assay showing MAPK4 phosphorylates AKT T308, replicated in cancer contexts, multiple orthogonal methods\",\n      \"pmids\": [\"30688659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MAPK4 activates the androgen receptor (AR) by enhancing GATA2 transcriptional expression and stabilizing GATA2 protein through repression of GATA2 ubiquitination and degradation. Concerted activation of both GATA2/AR and AKT pathways by MAPK4 promotes prostate cancer cell proliferation, anchorage-independent growth, xenograft growth, and castration resistance. Both pathways are necessary for MAPK4 tumor-promoting activity.\",\n      \"method\": \"Western blotting, ubiquitination assays, gene knockdown and overexpression, xenograft mouse models, CRPC patient sample correlation\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (ubiquitination assay, xenograft, patient correlation), replicated MAPK4-AKT axis from prior study, new GATA2/AR mechanism established\",\n      \"pmids\": [\"33586682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MAPK4 drives AKT activation independent of PI3K in a large subset of triple-negative breast cancer (TNBC) cells. MAPK4 expression is critical for TNBC cell and xenograft growth. Repressing MAPK4 sensitizes TNBC cells and xenografts to PI3K inhibitors by removing a PI3K-bypass mechanism for AKT activation.\",\n      \"method\": \"siRNA/shRNA knockdown, AKT phosphorylation assays, PI3K inhibitor drug sensitivity assays, xenograft mouse models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — xenograft models plus biochemical AKT activation assays and drug synergy experiments; consistent with established MAPK4-AKT mechanism\",\n      \"pmids\": [\"35017531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MAPK4 also enhances PDK1 protein synthesis, thereby phosphorylating/activating PDK1 substrates beyond AKT. This MAPK4-PDK1 axis cooperates with the MAPK4-AKT axis to promote tumor growth and confer resistance to both PI3K and PI3K/PDK1 co-blockade in TNBC cells.\",\n      \"method\": \"Protein synthesis assays, PDK1 substrate phosphorylation assays, siRNA knockdown, drug resistance assays in TNBC cell models\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — new mechanistic axis (MAPK4-PDK1) supported by biochemical and cell-based data, single lab, consistent with established MAPK4 biology\",\n      \"pmids\": [\"37531320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MAPK4 depletion in gastric cancer cells induces secretion of macrophage migration inhibitory factor (MIF), which polarizes tumor-associated macrophages (TAMs). In turn, TAMs activate epithelial-mesenchymal transition in gastric cancer cells and suppress MAPK4 expression, creating a positive feedback loop that facilitates liver metastasis in orthotopic mouse models.\",\n      \"method\": \"In vivo orthotopic mouse models, shRNA knockdown, cytokine measurement (MIF secretion), transcriptome profiling, tissue array analysis\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo orthotopic model with mechanistic feedback loop identified, single lab, multiple methods\",\n      \"pmids\": [\"36797541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MAPK4 knockout reduces AKT phosphorylation in cervical cancer cells, impairing DNA repair signaling (reduced p-DNA-PK and RAD51), which enhances radiation sensitivity and sensitivity to PARP1 inhibitors. Constitutively active AKT rescues DNA repair protein expression in MAPK4 KO cells, placing MAPK4 upstream of AKT in this DNA repair context.\",\n      \"method\": \"CRISPR knockout, western blotting, colony formation assay, immunofluorescence, xenograft mouse models, constitutively active AKT rescue experiments\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with AKT rescue experiment establishing pathway placement, supported by in vivo xenograft data, single lab\",\n      \"pmids\": [\"32711558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MAPK4 deficiency in mice reduces signaling through MK5, AKT, JNK, and p38 MAPK pathways in LPS-induced acute lung injury. MAPK4 KO mice show prolonged survival, reduced pro-inflammatory cytokines, and altered immune cell composition in bronchoalveolar lavage fluid. MAPK4 expression in macrophages is upregulated by LPS, and MAPK4 knockdown reduces pro-inflammatory cytokine expression in macrophages.\",\n      \"method\": \"MAPK4 knockout mice, LPS-induced ALI model, shRNA knockdown in macrophages, signaling pathway analysis by western blot, cytokine measurement\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with in vivo phenotype and defined signaling readouts, single lab\",\n      \"pmids\": [\"33088477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MAPK4 silencing in endothelial cells inhibits their proliferation and migration, and increases ERK1/2 pathway signaling (but not AKT or JNK). In vivo, targeted silencing of MAPK4 in endothelial cells using CD34 promoter-driven siRNA inhibits tumor angiogenesis and NSCLC growth, indicating MAPK4 facilitates angiogenesis partly by suppressing ERK1/2 signaling in endothelial cells.\",\n      \"method\": \"siRNA knockdown, flow cytometry, immunofluorescence, whole-genome transcriptional analysis, western blotting, in vivo tumor model with CD34 promoter-driven siRNA\",\n      \"journal\": \"Cancer innovation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo model with endothelial-cell-specific knockdown and defined ERK1/2 pathway readout, single lab\",\n      \"pmids\": [\"38947754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MAPK4 translocates to the nucleus in response to MC-LR exposure and binds to the GATA2 protein (residues 295-480), enhancing SNCA gene transcription and thereby increasing α-synuclein protein expression, contributing to Lewy body formation and Parkinson's-like pathology.\",\n      \"method\": \"Nuclear fractionation, co-immunoprecipitation of MAPK4 and GATA2, luciferase reporter assay for SNCA transcription, western blotting, in vitro and in vivo MC-LR exposure models\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — nuclear translocation plus direct GATA2 binding and SNCA transcription readout; single lab with multiple methods\",\n      \"pmids\": [\"39738876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MAPK4 inhibits PI3K-AKT-mTOR signaling in B cells by activating the IRF4-SHIP1 pathway. MAPK4 KO mice show enhanced proximal BCR signaling, heightened B cell proliferation, higher IL-6 production, and impaired marginal zone B cell differentiation. The MAPK4 agonist Vacquinol-1 enhances MZ B cell differentiation and reduces IL-6 secretion in collagen-induced arthritis models.\",\n      \"method\": \"MAPK4 knockout mice, pharmacological agonist (Vacquinol-1), flow cytometry, cytokine measurement, signaling pathway analysis by western blotting, collagen-induced arthritis model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined signaling pathway placement (IRF4-SHIP1 downstream of MAPK4), multiple readouts, single lab\",\n      \"pmids\": [\"39863600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FUS RNA binding protein stabilizes MAPK4 mRNA in TNBC cells, as shown by RNA immunoprecipitation. Puerarin treatment downregulates both FUS and MAPK4, and MAPK4 overexpression attenuates puerarin's anti-tumor effects, placing FUS upstream of MAPK4 in this regulatory axis.\",\n      \"method\": \"RNA immunoprecipitation (RIP) assay, western blotting, qRT-PCR, overexpression rescue experiments, xenograft mouse model\",\n      \"journal\": \"Chemical biology & drug design\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — RIP assay establishes FUS-MAPK4 mRNA interaction, rescue experiment supports pathway placement, single lab\",\n      \"pmids\": [\"39223105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A spermidine derivative (SPDD) weakens the interaction between MAPK4 and AKT, resulting in decreased AKT phosphorylation and reduced expression of IL-6, IL-1β, iNOS, and COX-2, thereby alleviating colitis. This places MAPK4 as a direct physical mediator of AKT activation in the inflammatory context.\",\n      \"method\": \"Co-immunoprecipitation (MAPK4-AKT interaction assay), RNA-seq, western blotting, DSS-induced colitis mouse model, Caco-2 cell inflammation model\",\n      \"journal\": \"Foods (Basel, Switzerland)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP assay in a pharmacological study; consistent with established MAPK4-AKT mechanism but single lab, single method for the mechanistic claim\",\n      \"pmids\": [\"40238233\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAPK4 (ERK4) is an atypical MAPK that is constitutively phosphorylated at its activation loop Ser186 by group I PAKs downstream of Rac1; phospho-Ser186 enables MAPK4 to bind MK5 via a novel FRIEDE docking motif, translocate MK5 to the cytoplasm, and directly phosphorylate/activate MK5, while DUSP2 dephosphorylates and inactivates this pathway. Beyond the MK5 axis, MAPK4 can non-canonically activate AKT by directly phosphorylating its T308 activation loop and by engaging mTORC2 for S473 phosphorylation independent of PI3K, and also enhances PDK1 protein synthesis, thereby cooperatively driving oncogenic AKT/mTOR signaling, AR activation via GATA2 stabilization, tumor angiogenesis, and inflammatory responses in multiple cancer and disease contexts.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAPK4 (ERK4) is an atypical, constitutively active MAP kinase that functions as a stable upstream activator of MK5 and, in disease contexts, as a non-canonical driver of oncogenic AKT signaling [#1, #8]. Its activation loop residue Ser186 within the SEG motif is phosphorylated in trans by an upstream kinase in resting cells rather than by autophosphorylation, and this phosphorylation stimulates intrinsic catalytic activity and gates the protein's signaling output [#2, #3]; group I PAKs (PAK1/2/3) acting downstream of Rac1 are the responsible kinases [#5]. Phospho-Ser186 enables MAPK4 to bind MK5 through a non-canonical FRIEDE docking motif in the L16 extension, anchoring MK5 in the cytoplasm and directly phosphorylating and activating it, while ERK3 dimerization cooperatively reinforces MK5 activation [#0, #4]. The dual-specificity phosphatase DUSP2 docks on the MAPK4 CD domain and dephosphorylates the activation loop, switching off the pathway [#7]. Separately, MAPK4 directly binds and phosphorylates AKT at Thr308 independent of PI3K and engages mTORC2 for Ser473 phosphorylation, and additionally enhances PDK1 protein synthesis, together driving anchorage-independent growth, tumor xenograft growth, and resistance to PI3K-pathway inhibitors across prostate and triple-negative breast cancers [#8, #10, #11]. In prostate cancer this AKT axis cooperates with MAPK4-mediated stabilization of GATA2 and androgen receptor activation to promote castration resistance [#9]. Genetic loss of Mapk4 in mice is compatible with viability and fertility but produces a depression-like behavioral phenotype, and Mapk4 also shapes inflammatory and angiogenic responses in multiple tissue contexts [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that the orphan atypical kinase ERK4 has a defined substrate by identifying MK5 as its binding partner and demonstrating catalysis-dependent activation, answering what ERK4 actually does.\",\n      \"evidence\": \"Reciprocal Co-IP, catalytically dead mutants, and siRNA knockdown with kinase activity readouts in HEK293/HeLa cells, replicated by two independent labs\",\n      \"pmids\": [\"16973613\", \"16971392\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The upstream kinase activating ERK4 was unknown\", \"Structural basis of the ERK4-MK5 interaction not yet defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved how ERK4 is regulated by showing that activation-loop Ser186 is phosphorylated in trans in resting cells and is required for MK5 binding, cytoplasmic anchoring, and activation.\",\n      \"evidence\": \"In vivo phosphorylation assays, phospho-mutant constructs, mobility-shift, Co-IP and localization assays across two studies\",\n      \"pmids\": [\"18248330\", \"18720373\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the upstream Ser186 kinase unresolved\", \"Why phosphorylation is constitutive rather than stimulus-induced not explained\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the molecular docking mechanism by identifying the non-canonical FRIEDE motif, not the canonical CD domain, as the MK5-binding interface gated by activation-loop phosphorylation.\",\n      \"evidence\": \"Peptide overlay assays, FRIEDE point mutagenesis, Co-IP, localization, and kinase activity assays\",\n      \"pmids\": [\"19473979\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of the phospho-gated FRIEDE switch\", \"Whether other partners use this docking site untested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified the long-sought upstream kinase, placing ERK4 in a Rac1-PAK-ERK4-MK5 signaling cascade.\",\n      \"evidence\": \"Biochemical kinase purification, in vitro kinase assays, siRNA of PAK1/2/3, and activated Rac1 expression\",\n      \"pmids\": [\"21177870\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological stimuli engaging Rac1-PAK to control ERK4 not mapped\", \"Tissue contexts where this cascade operates unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the organismal role of Mapk4 through knockout, revealing a non-redundant behavioral function distinct from Erk3.\",\n      \"evidence\": \"Targeted Mapk4 disruption in mice with developmental, physiological, and forced-swim behavioral phenotyping\",\n      \"pmids\": [\"20956558\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of the depression-like phenotype unexplained\", \"Whether the MK5 axis underlies the behavioral effect untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified the off-switch of the pathway by showing DUSP2 dephosphorylates the ERK4 activation loop via CD-domain docking, with reciprocal stabilization of DUSP2.\",\n      \"evidence\": \"Co-IP, direct binding, dephosphorylation assays, DUSP2 stability measurements, and MK5 activity readouts\",\n      \"pmids\": [\"28252035\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological signals controlling DUSP2-ERK4 engagement unknown\", \"Whether DUSP2 regulates the AKT branch untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Revealed a non-canonical oncogenic function by showing MAPK4 directly phosphorylates AKT T308 independent of PI3K and engages mTORC2 for S473, transforming cells.\",\n      \"evidence\": \"Co-IP, in vitro kinase assays, phospho-specific blotting, mutagenesis, xenografts, and TCGA correlation\",\n      \"pmids\": [\"30688659\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How MAPK4 recruits/activates mTORC2 mechanistically unresolved\", \"Relationship between the MK5 and AKT branches unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended the MAPK4-AKT axis to therapeutic vulnerabilities, placing MAPK4 upstream of AKT-dependent DNA repair and inflammatory/radiation responses.\",\n      \"evidence\": \"CRISPR KO with constitutively active AKT rescue in cervical cancer; knockout mice in LPS-induced acute lung injury with multi-pathway signaling readouts\",\n      \"pmids\": [\"32711558\", \"33088477\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect control of DNA repair factors not separated\", \"Tissue-specific kinase substrates beyond AKT undefined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established a second oncogenic branch in prostate cancer, showing MAPK4 stabilizes GATA2 and activates AR cooperatively with AKT to drive castration resistance.\",\n      \"evidence\": \"Ubiquitination assays, knockdown/overexpression, xenografts, and CRPC patient correlation\",\n      \"pmids\": [\"33586682\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which MAPK4 represses GATA2 ubiquitination unknown\", \"Whether GATA2 stabilization is kinase-dependent untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Generalized MAPK4 as a PI3K-bypass mechanism, demonstrating that its depletion sensitizes TNBC to PI3K inhibitors.\",\n      \"evidence\": \"siRNA/shRNA knockdown, AKT phosphorylation assays, PI3K inhibitor sensitivity, and xenografts\",\n      \"pmids\": [\"35017531\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Predictive biomarkers for MAPK4-driven PI3K resistance undefined\", \"Combination dosing strategies not optimized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Broadened MAPK4 oncogenic output beyond AKT by linking it to PDK1 protein synthesis and to a macrophage-driven metastatic feedback loop.\",\n      \"evidence\": \"Protein synthesis and PDK1 substrate assays with drug resistance studies in TNBC; orthotopic gastric cancer models with MIF/TAM profiling\",\n      \"pmids\": [\"37531320\", \"36797541\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How MAPK4 enhances PDK1 translation mechanistically unknown\", \"The MIF-TAM feedback effectors downstream of MAPK4 not fully defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Documented context-specific and nuclear functions of MAPK4 in angiogenesis and neurodegeneration, expanding its roles beyond cancer cell-intrinsic AKT signaling.\",\n      \"evidence\": \"Endothelial-specific CD34-driven siRNA in NSCLC tumor models with ERK1/2 readouts; nuclear fractionation, MAPK4-GATA2 Co-IP and SNCA reporter assays in MC-LR exposure models\",\n      \"pmids\": [\"38947754\", \"39738876\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How MAPK4 suppresses endothelial ERK1/2 mechanistically unknown\", \"Trigger and regulation of MAPK4 nuclear translocation undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed immunoregulatory and pharmacologically tractable roles, with MAPK4 restraining BCR/PI3K signaling via IRF4-SHIP1 and serving as a druggable AKT-interaction node in inflammation.\",\n      \"evidence\": \"Knockout mice with Vacquinol-1 agonist in arthritis models; Co-IP disruption by spermidine derivative in colitis models\",\n      \"pmids\": [\"39863600\", \"40238233\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation of MAPK4 inhibiting versus activating AKT across cell types unresolved\", \"The colitis MAPK4-AKT claim rests on a single Co-IP method\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MAPK4 switches between its MK5 axis and its AKT/PDK1/GATA2 axes, and what determines its opposing effects on AKT in different cell types, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the MAPK4-AKT or MAPK4-mTORC2 interaction\", \"Determinants of context-dependent positive versus negative regulation of PI3K-AKT undefined\", \"Whether the constitutive Rac1-PAK input controls the oncogenic branches untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 8]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 5, 8]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [9, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 8]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8, 9, 10]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [14, 17]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MK5\", \"DUSP2\", \"AKT1\", \"GATA2\", \"PAK1\", \"ERK3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}