{"gene":"MAP2K5","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":1995,"finding":"MEK5 was identified as a novel MEK family member that does not phosphorylate ERK1, ERK2, ERK3, JNK/SAPK, or p38, nor is it phosphorylated by Raf-1, c-Mos, or MEKK1, indicating it lies in a distinct MAP kinase pathway. Alternative splicing produces a 50-kDa alpha isoform (expressed in liver and brain, particulate) and a 40-kDa beta isoform (ubiquitously distributed, primarily cytosolic), with differential subcellular localization determined by a 23-amino-acid N-terminal domain in MEK5α.","method":"PCR cloning, substrate phosphorylation assays in vitro, subcellular fractionation, tissue distribution analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — original discovery with in vitro kinase assays and fractionation, foundational paper","pmids":["7499418"],"is_preprint":false},{"year":1999,"finding":"MEKK3 physically interacts with MEK5 (identified by yeast two-hybrid and confirmed by co-immunoprecipitation in mammalian cells), and a dominant-active MEKK3 stimulates BMK1/ERK5 activity through MEK5; MEKK3 kinase activity is required for growth-factor-mediated activation of endogenous BMK1.","method":"Yeast two-hybrid screen, co-immunoprecipitation, dominant-active/kinase-dead mutant expression","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP and epistasis with kinase-dead mutants, replicated in multiple cell systems","pmids":["10593883"],"is_preprint":false},{"year":1999,"finding":"The ERK5/MEK5 pathway is required for Raf-dependent cellular transformation; constitutively active MEK5 (MEK5DD) synergizes with Raf to transform NIH 3T3 cells. Endogenous Raf-1 binds specifically to endogenous ERK5 (not ERK2 or SAPK), and Raf-1 contributes to Ras activation of ERK5 through protein-protein interactions rather than catalytic activity.","method":"Co-immunoprecipitation, NIH 3T3 transformation assay, dominant-negative and constitutively active MEK5 mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — epistasis with defined mutants, transformation assay, reciprocal Co-IP","pmids":["10531364"],"is_preprint":false},{"year":2000,"finding":"MEKK2 binds MEK5 via yeast two-hybrid and co-immunoprecipitation, activates BMK1/ERK5 through MEK5, and does so to a greater extent than MEKK3. A dominant-negative MEK5 specifically blocks MEKK2-induced BMK1/ERK5 activation without affecting JNK, establishing MEK5 as a specific downstream effector of MEKK2 in the BMK1/ERK5 pathway.","method":"Yeast two-hybrid, co-immunoprecipitation, dominant-negative MEK5, kinase assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP and epistasis confirmed with dominant-negative constructs","pmids":["11073940"],"is_preprint":false},{"year":2001,"finding":"Constitutively active MEK5 in cardiomyocytes induces serial sarcomere assembly and an elongated hypertrophic morphology, and dominant-negative MEK5 specifically blocks LIF-induced elongation. Cardiac-specific expression of activated MEK5 in transgenic mice causes eccentric cardiac hypertrophy progressing to dilated cardiomyopathy and sudden death, establishing MEK5-ERK5 as the pathway mediating cytokine-induced serial sarcomere assembly.","method":"Adenoviral expression of CA/DN MEK5 in cardiomyocytes, transgenic mice, morphological analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — clean in vitro and in vivo loss/gain-of-function with specific phenotypic readout, replicated across models","pmids":["11387209"],"is_preprint":false},{"year":2001,"finding":"Atypical protein kinase C isoforms (aPKCs, zetaPKC and lambda/iotaPKC) interact with MEK5 in an EGF-inducible manner, and this interaction is required and sufficient for MEK5 activation in response to EGF. aPKCs activate the Jun promoter through the MEF2C element (an ERK5 target) via MEK5.","method":"Co-immunoprecipitation, dominant-negative and constitutively active constructs, reporter assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and epistasis in a single study","pmids":["11158308"],"is_preprint":false},{"year":2003,"finding":"The PB1 domains of MEKK2 and MEKK3 heterodimerize with the PB1 domain of MEK5 (but not with each other) both in vitro and in vivo. Deletion or mutation of the MEKK2 PB1 domain abolishes MEKK2-MEK5 complexes, and expression of the free MEKK2 or MEKK3 PB1 domain specifically inhibits ERK5 activation without affecting p38 or JNK pathways.","method":"In vitro PB1 domain binding, co-immunoprecipitation, mutagenesis, dominant-interference PB1 domain expression","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of PB1-PB1 interaction, mutagenesis, and cell-based epistasis","pmids":["12912994"],"is_preprint":false},{"year":2003,"finding":"Activation of the MEK5-ERK5 pathway causes phosphorylation and stabilization of c-Fos and Fra-1. ERK5 directly phosphorylates c-Fos at sites distinct from ERK1/2 phosphorylation sites, and the C-terminal half of ERK5 is necessary for maximal transactivation of c-Fos and Fra-1.","method":"Constitutively active MEK5, phosphorylation assays, transactivation reporter assays, truncation mutants of ERK5","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 — kinase assays with mutagenesis and functional reporter readouts in single study","pmids":["12622723"],"is_preprint":false},{"year":2003,"finding":"MEK5 overexpression in prostate cancer cells stimulates proliferation, motility, and invasion, markedly increases MMP-9 (but not MMP-2) mRNA expression, and activates AP-1 (but not NF-κB) transcription via the MMP-9 promoter, establishing MEK5 as an upstream regulator of MMP-9/AP-1 in prostate cancer invasion.","method":"MEK5 transfection, luciferase reporter assays, EMSA, invasion assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays including EMSA and reporter assays in a single study","pmids":["12618764"],"is_preprint":false},{"year":2004,"finding":"Endogenous MEK5 and ERK5 are localized predominantly in the nucleus in both resting and EGF-stimulated HeLa and Rat-1 cells, bound to detergent-resistant nuclear moieties, whereas their upstream activator MEKK2 is cytosolic at rest and translocates to the nucleus upon EGF stimulation.","method":"Immunofluorescence microscopy, in situ detergent extraction (NP-40), subcellular fractionation","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — direct localization experiments with multiple methods (fractionation, extraction, imaging) in multiple cell lines","pmids":["15075238"],"is_preprint":false},{"year":2004,"finding":"The NMR structure of the PKCiota PB1 domain reveals it adopts a ubiquitin fold with an OPCA motif forming an acidic surface that mediates interaction with the basic surface of target PB1 domains including MEK5, confirmed by mutational analysis.","method":"NMR structure determination, mutational analysis of protein-protein interaction","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with functional validation by mutagenesis","pmids":["15143057"],"is_preprint":false},{"year":2004,"finding":"CT-1-induced cardiac hypertrophy is mediated by the MEK5-ERK5 pathway: dominant-negative MEK5 suppresses CT-1-induced hypertrophy (protein synthesis, BNP secretion, cell surface area increase) while dominant-negative MEK1 does not, and CT-1 activates ERK5 phosphorylation that is blocked by SOCS1/3 overexpression.","method":"Adenoviral dominant-negative MEK5/MEK1, SOCS overexpression, phosphorylation assays, hypertrophy markers","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 — specific epistasis with DN-MEK5 vs. DN-MEK1, multiple readouts","pmids":["15623437"],"is_preprint":false},{"year":2005,"finding":"Targeted deletion of mek5 in mice results in embryonic lethality at ~E10.5 with abnormal cardiac development, decreased proliferation and increased apoptosis. In mek5-/- MEFs, MEK5 is required for ERK5 activation and for MEF2 transcriptional activity; MEK5 loss sensitizes cells to sorbitol-induced caspase-3 activation without affecting cell cycle progression.","method":"Knockout mice, MEF analysis, ERK5 kinase assays, caspase activity assays, MEF2 reporter assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — genetic knockout with multiple orthogonal mechanistic readouts in vivo and in vitro","pmids":["15601854"],"is_preprint":false},{"year":2005,"finding":"The MEK5-ERK5 cascade is activated in biliary epithelial cells of polycystic kidney (PCK) rats, driving aberrant proliferation; siRNA knockdown of MEK5 significantly inhibits this hyperproliferation, while MEK1/2 inhibitors (PD98059, U0126) are less effective, establishing MEK5-ERK5 as the primary proliferative pathway in biliary dysgenesis.","method":"siRNA knockdown, kinase phosphorylation assays, proliferation assays, pharmacological inhibitors","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown with pathway-specific pharmacological comparison","pmids":["15631999"],"is_preprint":false},{"year":2005,"finding":"In Xenopus, MEK5-ERK5 is required for neural differentiation downstream of SoxD and upstream of Xngnr1 (a proneural gene); morpholino knockdown of ERK5 or MEK5 reduces head structure and inhibits neural differentiation, and forced MEK5-ERK5 activation alone is sufficient to induce neural differentiation.","method":"Morpholino antisense knockdown, constitutively active MEK5 expression, in vivo Xenopus assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis (loss-of-function + gain-of-function) with defined pathway position in vivo","pmids":["16179948"],"is_preprint":false},{"year":2007,"finding":"MEKK2 and MEK5 PB1 domains form a front-to-back heterodimer via basic (MEKK2) and acidic (MEK5) surfaces; a C-terminal 34-amino-acid extension of the MEK5 PB1 domain encodes an ERK5 docking site required for MEK5 activation of ERK5. MEKK2 in its quiescent state preferentially binds MEK5; upon activation, MEKK2 also binds MKK7 via the acidic cluster of its PB1 domain to activate JNK.","method":"Domain interaction mapping, mutagenesis, co-immunoprecipitation, kinase assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis and domain reconstitution defining molecular mechanism","pmids":["17452462"],"is_preprint":false},{"year":2007,"finding":"NMR solution structure of MEKK3 PB1 domain reveals a ubiquitin fold with cis/trans prolyl isomerization at Gln38-Pro39; MEKK3 PB1 binds MEK5 PB1 with Kd ~10^-8 M, with Lys7 and Arg5 of the basic cluster being critical for MEK5 PB1 interaction.","method":"NMR structure determination, backbone dynamics, mutagenesis, binding affinity measurement","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with mutagenesis defining binding mechanism","pmids":["17985933"],"is_preprint":false},{"year":2008,"finding":"Constitutively active MEK5α inhibits ERK5 SUMOylation (at K6/K22) independently of its kinase activity but dependent on MEK5-ERK5 physical association, thereby preventing Ubc9/PIAS1-mediated SUMOylation that suppresses ERK5 transcriptional activity; H2O2 and high glucose induce ERK5 SUMOylation and reduce its transcriptional activity.","method":"CA-MEK5α transgenic mice, SUMOylation-site mutants (K6R/K22R), siRNA-PIAS1, DN-Ubc9, cardiac function assays","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis of SUMOylation sites, identification of writer (Ubc9/PIAS1), transgenic mouse validation","pmids":["18467627"],"is_preprint":false},{"year":2008,"finding":"Pharmacological inhibitors BIX02188 and BIX02189 inhibit purified MEK5 enzymatic activity and selectively block ERK5 phosphorylation without affecting ERK1/2 phosphorylation in sorbitol-stimulated cells; they also inhibit MEF2C transcriptional activation downstream of MEK5/ERK5.","method":"In vitro kinase assay with purified MEK5, cell-based ERK5/ERK1/2 phosphorylation assays, MEF2C reporter assay","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — purified enzyme assay with selectivity demonstration in cells","pmids":["18834865"],"is_preprint":false},{"year":2008,"finding":"MEK5-BMK1 (ERK5), but not MEK1-ERK1/2, mediates fluid shear stress inhibition of TNF-induced JNK activation in endothelial cells; selective MEK5 inhibitor BIX02188 completely reverses flow-mediated inhibition of JNK, while MEK1/2-selective concentrations of PD184352 have no effect.","method":"Pharmacological inhibitors at selective concentrations, shear stress apparatus, JNK activation assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — pathway epistasis using selective inhibitors with defined mechanism","pmids":["18358237"],"is_preprint":false},{"year":2008,"finding":"MEK5/ERK5 activation promotes an epithelial-to-mesenchymal transition (EMT) phenotype in breast cancer cells, with upregulation of vimentin, SNAI2 (slug), ZEB1, and N-cadherin, and downregulation of E-cadherin and keratins; shRNA targeting ERK5 reverses MEK5-mediated EMT gene expression.","method":"MEK5 overexpression, proteomics (2D-gel/LC-MS/MS), ERK5 shRNA knockdown, immunofluorescence","journal":"Breast cancer research : BCR","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (proteomics + shRNA rescue) in single study","pmids":["19087274"],"is_preprint":false},{"year":2008,"finding":"MEK5-ERK5 regulates thymocyte apoptosis but not positive selection; retroviral dominant-negative MEK5 in developing thymocytes increases apoptosis while constitutively active MEK5 reduces it; ERK5 activity correlates with Nur77 family member levels (but not Bim) as effectors of thymocyte apoptosis.","method":"Retroviral expression of DN/CA MEK5 in thymocytes, apoptosis assays, Nur77/Bim expression analysis","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 — gain-of-function and loss-of-function with pathway effector identification","pmids":["18548009"],"is_preprint":false},{"year":2009,"finding":"MEK5/ERK5 signaling downstream of VEGF induces Id1 and suppresses thrombospondin-1 (TSP1) expression to promote angiogenesis; Epac/Rap1 antagonizes this by suppressing Id1 and inducing TSP1, establishing MEK5 as a pro-angiogenic component controlling Id1/TSP1 balance.","method":"MEK5 knockdown/overexpression, TSP1 and Id1 expression assays, in vivo angiogenesis assay, Epac/Rap1 activation","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal experiments defining pathway position and effectors","pmids":["19710505"],"is_preprint":false},{"year":2009,"finding":"Constitutive MEK5/ERK5 activation strongly inhibits endothelial cell migration and increases focal contact number and size via decreased expression of p130Cas (a key regulator of focal contact turnover); this results in increased cell rigidity and reduced motility.","method":"Retroviral CA-MEK5 expression, migration assays, focal contact imaging, p130Cas expression analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — defined molecular effector (p130Cas) with functional migration readout","pmids":["19605361"],"is_preprint":false},{"year":2009,"finding":"MEK5 and ERK5 are required for the pro-myogenic actions of IGF-2; dominant-negative MEK5 blocks IGF-2-induced myogenesis and dominant-negative ERK5 prevents nuclear localization of ERK5-GFP upon MEK5 activation; constitutively active MEK5 rescues defects caused by antisense Igf2.","method":"CA/DN MEK5 expression, ERK5-GFP live imaging, kinase activity assays, myogenic reporter assays","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — gain-of-function rescue and loss-of-function with live imaging of ERK5 translocation","pmids":["19654213"],"is_preprint":false},{"year":2011,"finding":"MEK5 is activated by laminar shear stress in human dermal microvascular endothelial cells, activates ERK5, and induces KLF4 expression (in an ERK5-dependent manner); MEK5/ERK5/KLF4 signaling reduces endothelial inflammatory responses to TNF, in part mediated by KLF4.","method":"Laminar shear stress, constitutively active MEK5 expression, siRNA knockdown of ERK5 and KLF4, Western blotting, microarray","journal":"Microcirculation (New York, N.Y. : 1994)","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis with siRNA knockdown and CA mutants defining pathway order","pmids":["21166929"],"is_preprint":false},{"year":2014,"finding":"XIAP directly interacts with MEKK2/3 and competes with PB1 domain-mediated binding to MEK5. XIAP and cIAP1 conjugate predominantly K63-linked ubiquitin chains to MEKK2 and MEKK3, which directly impedes MEK5-ERK5 interaction in a trimeric complex, leading to ERK5 inactivation; loss of XIAP or cIAP1 causes ERK5 hyperactivation and promotes myoblast differentiation via MEKK2/3-ERK5.","method":"Co-immunoprecipitation, ubiquitination assays, ubiquitin linkage analysis, XIAP/cIAP1 knockdown/knockout, myoblast differentiation assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — reconstituted ubiquitination mechanism with defined linkage type, competition assay, and cellular phenotype validation","pmids":["24975362"],"is_preprint":false},{"year":2014,"finding":"miR-143 directly represses MAP2K5 mRNA, modulating MAP2K5-ERK5 signaling during adipogenic differentiation of adipose-derived stromal cells; the stage-specific effect of miR-143 on adipogenesis is dependent on MAP2K5 suppression.","method":"miRNA overexpression, luciferase reporter assay for direct targeting, knockdown/overexpression of MAP2K5","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — direct targeting confirmed by reporter assay with functional differentiation readout","pmids":["24448661"],"is_preprint":false},{"year":2017,"finding":"YAP promotes myogenic differentiation via MEK5-ERK5 by activating the Abl/Src/MEKK3/MEK5/ERK5 cascade; co-immunoprecipitation shows YAP interacts with MEKK3 and ERK5; site-directed mutagenesis of MEKK3 Y181F (disrupting the PPGY/YAP interaction motif) inhibits MEK5/ERK5 activation and myogenic differentiation.","method":"Co-immunoprecipitation, constitutively active MEK5 expression, site-directed mutagenesis, inhibitor studies, myogenic differentiation assays","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with mutagenesis defining interaction motif and functional consequence","pmids":["28356344"],"is_preprint":false},{"year":2018,"finding":"MAP2K5 variants A321T and M367T (located in the kinase domain) consistently phosphorylate ERK5 at Ser731+Thr733 or Ser496, promoting ERK5 nuclear translocation and altering downstream gene expression, resulting in thyroid epithelial cell malignant transformation.","method":"Functional study of kinase domain variants, ERK5 phosphorylation assays, nuclear translocation assays, cell transformation assays","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 — functional validation of specific kinase domain mutations with phosphorylation site identification","pmids":["30132833"],"is_preprint":false},{"year":2018,"finding":"KRAS suppression-induced MYC degradation is antagonized by an ERK1/2-inhibition-induced feedforward mechanism involving EGFR and SRC leading to ERK5 (via MEK5) activation and phosphorylation of MYC at S62, preventing its degradation; concurrent ERK1/2 and ERK5 inhibition causes synergistic MYC loss and PDAC growth suppression.","method":"Kinome-wide proteomics screen, high-throughput MYC degradation screen, ERK5/MEK5 inhibitors, phospho-MYC S62 assays, PDAC cell growth assays","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 1 — identified specific phosphorylation site (S62) on MYC by MEK5-ERK5, validated by multiple screens and pharmacological approaches","pmids":["30423298"],"is_preprint":false},{"year":2019,"finding":"Resistance to ERK inhibitors (SCH772984) and BRAF/MEK inhibitors in melanoma involves activation of the IGF1R-MEK5-ERK5 signaling pathway, which counteracts inhibition of ERK1/2 activation; IGF1R inhibition blocks ERK5 activation in resistant cells and reduces growth in 3D spheroids and in vivo.","method":"Drug-resistant cell line generation, ERK5/ERK1/2 phosphorylation assays, IGF1R inhibition, 3D spheroid assays, xenograft models","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — defined pathway (IGF1R→MEK5→ERK5) with pharmacological epistasis and in vivo validation","pmids":["30833419"],"is_preprint":false},{"year":2019,"finding":"MEK5 knockdown in prostate cancer cells impairs phosphorylation of the catalytic subunit of DNA-PK at Ser2056 in response to ionizing radiation or etoposide, delays resolution of γH2AX and 53BP1 foci, and compromises nonhomologous end joining (NHEJ) repair, sensitizing cells to genotoxic stress.","method":"MEK5 siRNA knockdown, DNA-PK phosphorylation assays, γH2AX/53BP1 foci imaging, NHEJ cell-based assay, clonogenic survival, xenograft experiments","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including NHEJ assay, phosphorylation, foci dynamics, and in vivo validation","pmids":["31980741"],"is_preprint":false},{"year":2020,"finding":"The MEK5-ERK5 axis controls lipid metabolism in small-cell lung cancer, including the mevalonate/cholesterol synthesis pathway; depletion of MEK5/ERK5 perturbs lipid metabolism pathways and sensitizes SCLC cells to statin treatment.","method":"MEK5/ERK5 knockdown, transcriptomics, lipidomics, pharmacological inhibition, in vitro and in vivo growth assays","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — transcriptomics and lipidomics with functional validation in vitro and in vivo","pmids":["31969375"],"is_preprint":false},{"year":2020,"finding":"MEK5/ERK5 signaling mediates IL-4-induced M2 macrophage differentiation through regulation of c-Myc expression; ERK5 activation is required for M2 marker induction (Arg-1, Ym-1, Fizz-1) via c-Myc, independently of STAT3 or STAT6 phosphorylation, confirmed by myeloid-specific Erk5 knockout mice.","method":"MEK5 inhibitor, ERK5 inhibitor, myeloid-specific Erk5 conditional knockout (LysMcre/Erk5f/f), STAT3/6 phosphorylation assays, c-Myc expression analysis","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 2 — conditional knockout mouse model with pharmacological and genetic validation, pathway effector (c-Myc) identified","pmids":["32745297"],"is_preprint":false},{"year":2020,"finding":"The MEKK3-MEK5-ERK5 kinase cascade is required for basal mitochondrial degradation (independent of exogenous damage); genetic or pharmacological inhibition of MEK5 or ERK5 increases mitochondrial content by reducing lysosome-mediated mitochondrial degradation, without affecting bulk autophagy, PINK1-Parkin mitophagy, or mitochondrial biogenesis.","method":"Genetic inhibition (CRISPR/knockout), pharmacological inhibitors, mitochondrial content quantification, lysosome-mediated degradation assays","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 — genetic and pharmacological approaches with specific mechanistic readouts distinguishing from other pathways","pmids":["33101709"],"is_preprint":false},{"year":2021,"finding":"MEK5 inhibition in neuronal cells reduces p62 levels and increases LC3-II/LC3-I ratio (autophagy activation) in an mTOR- and ERK5-independent manner; MEK5 inhibition alleviates TDP-43 mislocalization and cell death in TDP-43-expressing neuronal cells, identifying MEK5 as a novel autophagy modulator.","method":"MEK5 inhibitor (BIX02188), autophagy markers (p62, LC3), mTOR assays, TDP-43 localization imaging","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological inhibition with multiple autophagy markers revealing ERK5-independent mechanism","pmids":["31005259"],"is_preprint":false},{"year":2021,"finding":"The Hedgehog-GLI pathway regulates MEK5 and ERK5 expression in melanoma: GLI1 binds a non-canonical GLI consensus sequence at the MAPK7 (ERK5) promoter (confirmed by chromatin immunoprecipitation), and ERK5 is required for Hedgehog-GLI-dependent melanoma cell proliferation.","method":"Chromatin immunoprecipitation, GLI1 genetic inhibition (Patched-1 knockdown), ERK5 inhibition, proliferation assays","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP defining transcriptional regulation with functional epistasis","pmids":["34681917"],"is_preprint":false},{"year":2021,"finding":"Map2k5 knockout mice display dopaminergic cell loss and decreased tyrosine hydroxylase in the nigrostriatal pathway, with behavioral phenotypes including decreased locomotion, coordination defects, and impaired prepulse inhibition, establishing MAP2K5 as a regulator of dopaminergic neuron survival in vivo.","method":"Targeted Map2k5 knockout mouse model, behavioral testing, immunohistochemistry for tyrosine hydroxylase","journal":"Frontiers in aging neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo knockout with specific neurochemical and behavioral phenotypes","pmids":["34168549"],"is_preprint":false},{"year":2025,"finding":"MEK5-ERK5 activates the Hedgehog-GLI signaling pathway in melanoma: constitutively active MEK5 (MEK5DD) potentiates GLI transcriptional activity and increases GLI1/GLI2 protein levels; ERK5 silencing reduces GLI1/GLI2 mRNA and protein and inhibits GLI transcriptional activity; combined GLI and MEK5 inhibitors more effectively reduce melanoma spheroid growth.","method":"ERK5 shRNA, MEK5/ERK5 pharmacological inhibitors (JWG-071, AX15836, GW284543, BIX02189), MEK5DD overexpression, GLI luciferase reporter assay, 3D spheroid assays","journal":"Cellular oncology","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal gain/loss-of-function with reporter assay defining pathway regulation","pmids":["39998753"],"is_preprint":false},{"year":2025,"finding":"MAPKi/ERK5i co-inhibition in NRAS-mutant melanoma induces sustained G1 cell cycle arrest by suppressing Cyclin D1 and CDK4; forced expression of Cyclin D1 and CDK4 rescues cell cycle progression, identifying Cyclin D/CDK4 as the key mediators of the combined MEKi/ERK5i anti-proliferative effect.","method":"Transcriptome analysis, MEKi/ERK5i pharmacological inhibitors, Cyclin D1/CDK4 forced expression rescue, cell cycle analysis","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — rescue experiment with defined molecular effectors and transcriptome support","pmids":["41053077"],"is_preprint":false},{"year":2025,"finding":"RBM39 (a splicing factor) maintains full-length MEK5 mRNA splicing; RBM39 knockdown causes mis-splicing of MEK5, generating aberrant isoforms with exon loss that lack kinase function and undergo proteasomal degradation, thereby inhibiting MM cell survival. Full-length MEK5 activity maintains MM cell survival via p65/NF-κB.","method":"RBM39 knockdown, indisulam-mediated RBM39 degradation, splicing analysis, MEK5 isoform characterization, proteasome inhibition, p65 activity assays","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 — defined splicing-dependent regulation of MEK5 function with downstream effector identification","pmids":["40048740"],"is_preprint":false}],"current_model":"MAP2K5 (MEK5) is a dual-specificity MAP kinase kinase that functions as the obligate, specific activator of ERK5 (BMK1) within a three-tier cascade in which MEKK2 or MEKK3 (bound to MEK5 via PB1 domain heterodimerization) phosphorylate and activate MEK5, which in turn phosphorylates and activates ERK5; this pathway is activated by growth factors, cytokines, oxidative stress, and fluid shear stress to regulate cardiac sarcomere assembly, neural differentiation, thymocyte apoptosis, endothelial anti-inflammatory responses, M2 macrophage differentiation, basal mitochondrial degradation, myogenesis, and cell survival, with ERK5 activity subject to negative regulation by MEKK2/3 ubiquitination by XIAP/cIAP1 and by SUMOylation at K6/K22 (promoted by Ubc9/PIAS1 and antagonized by MEK5 association), while nuclear-localized MEK5 and ERK5 transmit signals to transcription factors including MEF2, c-Fos/Fra-1, KLF4, and NF-κB, and MEK5 also controls DNA repair (NHEJ via DNA-PK), lipid/cholesterol metabolism, MYC stability (via S62 phosphorylation by ERK5), and Hedgehog-GLI pathway activation."},"narrative":{"teleology":[{"year":1995,"claim":"Identification of MEK5 as a novel MAP kinase kinase in a distinct signaling module resolved the question of whether additional MAPK cascades existed beyond the ERK1/2, JNK, and p38 pathways, revealing two splice isoforms (α and β) with distinct subcellular distributions.","evidence":"PCR cloning, in vitro substrate phosphorylation assays, and subcellular fractionation in multiple tissues","pmids":["7499418"],"confidence":"High","gaps":["The specific MAPK substrate of MEK5 was not yet identified","No upstream kinase activating MEK5 was known","Physiological roles were undefined"]},{"year":1999,"claim":"Identification of MEKK3 and Raf-1 as upstream regulators of the MEK5–ERK5 cascade established the three-tier architecture of this pathway and its link to Ras-driven transformation.","evidence":"Yeast two-hybrid, co-immunoprecipitation, dominant-active/kinase-dead MEKK3 mutants, NIH 3T3 transformation assay with constitutively active MEK5","pmids":["10593883","10531364"],"confidence":"High","gaps":["The molecular basis of MEKK3–MEK5 binding was unknown","Whether MEKK2 also activates MEK5 was untested"]},{"year":2000,"claim":"Demonstration that MEKK2 binds and activates MEK5–ERK5 more potently than MEKK3 broadened the upstream input map and showed MEK5 is the specific mediator of MEKK2-to-ERK5 signaling.","evidence":"Yeast two-hybrid, co-immunoprecipitation, dominant-negative MEK5 selectively blocking MEKK2-induced ERK5 without affecting JNK","pmids":["11073940"],"confidence":"High","gaps":["Structural basis for MEKK2/3 selectivity for MEK5 over other MKKs was unclear"]},{"year":2001,"claim":"Constitutive MEK5 activation in cardiomyocytes induced serial sarcomere assembly and eccentric hypertrophy progressing to dilated cardiomyopathy in transgenic mice, establishing the first in vivo physiological role for MEK5–ERK5 signaling.","evidence":"Adenoviral CA/DN MEK5 in cardiomyocytes, cardiac-specific MEK5 transgenic mice with morphological and functional cardiac analysis","pmids":["11387209"],"confidence":"High","gaps":["Whether endogenous MEK5 is essential for cardiac development required loss-of-function genetics","Downstream transcriptional effectors in the heart were not defined"]},{"year":2003,"claim":"PB1-domain-mediated heterodimerization was identified as the structural mechanism coupling MEKK2/3 to MEK5, with specificity encoded by complementary basic (MEKK2/3) and acidic (MEK5) surfaces on ubiquitin-fold PB1 domains.","evidence":"In vitro PB1 domain binding, co-immunoprecipitation, mutagenesis of PB1 domains, dominant-interference experiments, NMR structures","pmids":["12912994","15143057","17985933"],"confidence":"High","gaps":["Full-length MEKK2/3–MEK5–ERK5 ternary complex structure was not resolved","How PB1 domain interaction is regulated dynamically in cells was unclear"]},{"year":2003,"claim":"MEK5–ERK5 was shown to regulate transcription factor outputs including c-Fos/Fra-1 stabilization and AP-1/MMP-9 transcription, connecting the pathway to gene expression programs for invasion and proliferation.","evidence":"CA-MEK5, phosphorylation assays, reporter assays, EMSA, invasion assays in prostate cancer cells","pmids":["12622723","12618764"],"confidence":"Medium","gaps":["Direct ERK5 phosphorylation sites on c-Fos were mapped but not confirmed by mass spectrometry","Whether MEK5 regulates AP-1 independently of ERK5 was not addressed"]},{"year":2004,"claim":"Endogenous MEK5 and ERK5 were found to reside predominantly in the nucleus bound to detergent-resistant structures, revising the assumption that the cascade signals only from the cytoplasm.","evidence":"Immunofluorescence, in situ NP-40 extraction, subcellular fractionation in HeLa and Rat-1 cells","pmids":["15075238"],"confidence":"High","gaps":["Nuclear substrates of MEK5 beyond ERK5 were not identified","Whether nuclear MEK5 has kinase-independent scaffolding functions was untested"]},{"year":2005,"claim":"Genetic knockout of Mek5 proved it is essential for embryonic viability and cardiac development, and demonstrated that MEK5 is the non-redundant upstream activator of ERK5 and MEF2 transcriptional activity, with a pro-survival role against stress-induced apoptosis.","evidence":"Mek5 knockout mice (lethal ~E10.5), MEF analysis of ERK5 activation, MEF2 reporter assays, caspase-3 activity assays","pmids":["15601854"],"confidence":"High","gaps":["Conditional knockouts in specific tissues were not yet available","Whether other kinases partially compensate in non-cardiac tissues was unclear"]},{"year":2005,"claim":"MEK5–ERK5 was positioned as a key driver of neural differentiation downstream of SoxD in Xenopus, demonstrating conservation of its developmental signaling role across vertebrates.","evidence":"Morpholino knockdown of MEK5/ERK5 and constitutively active MEK5 in Xenopus embryos","pmids":["16179948"],"confidence":"High","gaps":["Direct phosphorylation targets of ERK5 in neural progenitors were not identified","Whether MEK5 has mammalian neural differentiation roles was not yet shown in knockout models"]},{"year":2007,"claim":"Detailed domain mapping revealed that a 34-amino-acid extension C-terminal to the MEK5 PB1 domain encodes the ERK5 docking site, and that MEKK2 switches between MEK5 and MKK7 binding upon activation, explaining how the PB1 module achieves pathway specificity.","evidence":"Domain interaction mapping, mutagenesis, co-immunoprecipitation, kinase assays","pmids":["17452462"],"confidence":"High","gaps":["Atomic-resolution structure of the MEK5 PB1-ERK5 docking interaction was not solved","How activation-dependent conformational change in MEKK2 triggers partner switching was not mechanistically defined"]},{"year":2008,"claim":"MEK5 was shown to antagonize ERK5 SUMOylation at K6/K22 through physical association (independently of its kinase activity), while BIX02188/BIX02189 were validated as selective MEK5 catalytic inhibitors, providing both a kinase-independent regulatory mechanism and pharmacological tools.","evidence":"SUMOylation-site mutants, siRNA-PIAS1, DN-Ubc9, transgenic mice; purified MEK5 in vitro kinase assays with BIX compounds, cell-based selectivity assays","pmids":["18467627","18834865"],"confidence":"High","gaps":["Whether SUMOylation-regulated ERK5 activity and kinase-dependent ERK5 activity converge on the same targets was unclear","BIX compound selectivity against the full kinome was not comprehensively profiled"]},{"year":2008,"claim":"MEK5–ERK5 was identified as the pathway mediating flow-mediated inhibition of JNK in endothelial cells and as a driver of EMT in breast cancer, expanding its roles to vascular mechanotransduction and cancer metastasis.","evidence":"Selective MEK5 inhibitor BIX02188 in shear stress assays; MEK5 overexpression with proteomics and ERK5 shRNA in breast cancer cells","pmids":["18358237","19087274"],"confidence":"Medium","gaps":["Direct endothelial substrates of ERK5 mediating JNK crosstalk were not identified","EMT gene regulation by ERK5 was correlative without defined direct transcriptional targets"]},{"year":2011,"claim":"MEK5/ERK5 was shown to induce KLF4 in endothelial cells under shear stress, establishing a transcription factor link to anti-inflammatory vascular protection.","evidence":"Laminar shear stress, CA-MEK5, siRNA knockdown of ERK5 and KLF4 in dermal microvascular endothelial cells","pmids":["21166929"],"confidence":"Medium","gaps":["Whether ERK5 directly phosphorylates KLF4 or acts through intermediate transcription factors was not determined"]},{"year":2014,"claim":"XIAP/cIAP1-mediated K63-linked ubiquitination of MEKK2/3 was identified as a negative regulatory mechanism that disrupts the MEKK2/3–MEK5–ERK5 trimeric complex, adding an E3-ligase-based layer of pathway control relevant to myoblast differentiation.","evidence":"Ubiquitination assays with linkage analysis, competition binding experiments, XIAP/cIAP1 knockdown/knockout, myoblast differentiation assay","pmids":["24975362"],"confidence":"High","gaps":["Whether other E3 ligases regulate the same complex was not tested","Deubiquitinase(s) counteracting this modification were not identified"]},{"year":2018,"claim":"MEK5–ERK5 was shown to stabilize MYC via ERK5-mediated S62 phosphorylation in PDAC, revealing a feedforward survival mechanism activated when ERK1/2 is inhibited.","evidence":"Kinome-wide proteomics, high-throughput MYC degradation screen, MEK5/ERK5 inhibitors, phospho-MYC S62 assays in PDAC cells","pmids":["30423298"],"confidence":"High","gaps":["Whether this MEK5–ERK5–MYC axis operates in non-PDAC contexts was not established","Direct ERK5-MYC phosphorylation was shown but in vitro kinase assay with purified components was not presented"]},{"year":2019,"claim":"MEK5 was found to promote DNA-PK Ser2056 phosphorylation and nonhomologous end joining (NHEJ) repair, revealing a role in the DNA damage response independent of its canonical ERK5 transcriptional outputs.","evidence":"MEK5 siRNA knockdown, DNA-PK phosphorylation assays, γH2AX/53BP1 foci kinetics, cell-based NHEJ assay, clonogenic survival, xenograft validation","pmids":["31980741"],"confidence":"High","gaps":["Whether MEK5 regulates DNA-PK directly or through ERK5 was not resolved","The phosphorylation event linking MEK5 to DNA-PK Ser2056 was not reconstituted in vitro"]},{"year":2020,"claim":"MEK5–ERK5 was shown to control M2 macrophage differentiation via c-Myc (independent of STAT3/6) and to maintain basal mitochondrial degradation through lysosome-mediated turnover, expanding the pathway's roles to innate immunity and organelle homeostasis.","evidence":"Myeloid-specific Erk5 conditional knockout mice, MEK5/ERK5 inhibitors, CRISPR knockout, mitochondrial content quantification, lysosome degradation assays","pmids":["32745297","33101709"],"confidence":"High","gaps":["The mitochondrial substrate or receptor targeted by ERK5 for lysosomal degradation was not identified","Whether MEK5 has ERK5-independent roles in macrophage polarization was not tested"]},{"year":2021,"claim":"Map2k5 knockout mice showed dopaminergic neuron loss and motor/sensorimotor gating deficits, establishing an in vivo requirement for MEK5 in dopaminergic neuron survival and extending the pathway beyond developmental neurobiology to neurodegeneration-relevant phenotypes.","evidence":"Targeted Map2k5 knockout mouse model, behavioral testing, tyrosine hydroxylase immunohistochemistry","pmids":["34168549"],"confidence":"Medium","gaps":["Mechanism of dopaminergic cell death (apoptosis vs. other) was not defined","Whether ERK5 activation is reduced in these knockout brains was not directly shown","Single study without independent replication"]},{"year":2025,"claim":"MEK5–ERK5 was shown to activate the Hedgehog-GLI pathway in melanoma and to cooperate with ERK1/2 to maintain Cyclin D1/CDK4 expression, while full-length MEK5 mRNA integrity was found to depend on the splicing factor RBM39 for NF-κB-mediated survival in myeloma.","evidence":"MEK5DD overexpression, ERK5 shRNA, GLI reporter assays, 3D spheroid assays; MEKi/ERK5i co-inhibition with Cyclin D1/CDK4 rescue; RBM39 knockdown/degradation with splicing analysis and p65 activity assays","pmids":["39998753","41053077","40048740"],"confidence":"Medium","gaps":["Whether ERK5 directly phosphorylates GLI1/2 was not established","The exact mis-spliced MEK5 isoforms from RBM39 loss require further characterization","Whether combined MEKi/ERK5i approaches have clinical efficacy is unknown"]},{"year":null,"claim":"Critical mechanistic gaps remain: no high-resolution structure of a full-length MEKK2/3–MEK5–ERK5 ternary complex exists; the mechanism by which MEK5 regulates DNA-PK in NHEJ has not been reconstituted biochemically; the mitochondrial targets for MEK5–ERK5-dependent basal mitophagy are unknown; and the kinase-independent scaffolding functions of nuclear MEK5 are poorly characterized.","evidence":"","pmids":[],"confidence":"High","gaps":["Full-length ternary complex structure","Biochemical reconstitution of MEK5-to-DNA-PK signaling","Identity of mitochondrial degradation substrate/receptor","Kinase-independent nuclear functions of MEK5"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,12,18,29]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,18]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,3,6,12,15,18]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[4,12,14]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[32]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[40]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[34]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[12,21]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[33]}],"complexes":["MEKK2–MEK5–ERK5","MEKK3–MEK5–ERK5"],"partners":["MAPK7","MAP3K2","MAP3K3","XIAP","BIRC2","PRKCZ","PRKCI"],"other_free_text":[]},"mechanistic_narrative":"MAP2K5 (MEK5) is a dual-specificity MAP kinase kinase that serves as the obligate and specific activator of ERK5/BMK1, transducing signals from MEKK2/MEKK3 through PB1-domain-mediated heterodimerization to regulate cell survival, differentiation, cardiac development, and stress responses [PMID:7499418, PMID:12912994, PMID:15601854]. MEKK2 and MEKK3 bind MEK5 via front-to-back PB1 domain interactions (Kd ~10⁻⁸ M), with a C-terminal extension of the MEK5 PB1 domain encoding an ERK5 docking site essential for substrate activation; this cascade is negatively regulated by XIAP/cIAP1-mediated K63-linked ubiquitination of MEKK2/3, which disrupts the MEK5–ERK5 interaction [PMID:17452462, PMID:17985933, PMID:24975362]. MEK5-activated ERK5 phosphorylates transcription factors including MEF2C, c-Fos/Fra-1, and KLF4, and stabilizes MYC via S62 phosphorylation; MEK5 also promotes DNA-PK-dependent NHEJ repair, controls lipid/cholesterol metabolism, drives M2 macrophage differentiation through c-Myc, and maintains basal mitochondrial degradation [PMID:12622723, PMID:30423298, PMID:31980741, PMID:32745297, PMID:33101709, PMID:31969375]. Targeted deletion of Mek5 in mice causes embryonic lethality at ~E10.5 with cardiac defects, and Map2k5 knockout mice exhibit dopaminergic neuron loss with motor and sensorimotor gating deficits [PMID:15601854, PMID:34168549]."},"prefetch_data":{"uniprot":{"accession":"Q13163","full_name":"Dual specificity mitogen-activated protein kinase kinase 5","aliases":["MAPK/ERK kinase 5","MEK 5"],"length_aa":448,"mass_kda":50.1,"function":"Acts as a scaffold for the formation of a ternary MAP3K2/MAP3K3-MAP3K5-MAPK7 signaling complex. Activation of this pathway appears to play a critical role in protecting cells from stress-induced apoptosis, neuronal survival and cardiac development and angiogenesis. As part of the MAPK/ERK signaling pathway, acts as a negative regulator of apoptosis in cardiomyocytes via promotion of STUB1/CHIP-mediated ubiquitination and degradation of ICER-type isoforms of CREM (By similarity)","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q13163/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MAP2K5","classification":"Not Classified","n_dependent_lines":18,"n_total_lines":1208,"dependency_fraction":0.014900662251655629},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MAP2K5","total_profiled":1310},"omim":[{"mim_id":"612853","title":"RESTLESS LEGS SYNDROME, SUSCEPTIBILITY TO, 7; RLS7","url":"https://www.omim.org/entry/612853"},{"mim_id":"611122","title":"ANKYRIN REPEAT DOMAIN-CONTAINING PROTEIN 28; ANKRD28","url":"https://www.omim.org/entry/611122"},{"mim_id":"609487","title":"MITOGEN-ACTIVATED PROTEIN KINASE KINASE KINASE 2; MAP3K2","url":"https://www.omim.org/entry/609487"},{"mim_id":"602520","title":"MITOGEN-ACTIVATED PROTEIN KINASE KINASE 5; MAP2K5","url":"https://www.omim.org/entry/602520"},{"mim_id":"602016","title":"KLF TRANSCRIPTION FACTOR 2; KLF2","url":"https://www.omim.org/entry/602016"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Microtubules","reliability":"Approved"},{"location":"Primary cilium","reliability":"Approved"},{"location":"Nucleoli","reliability":"Additional"},{"location":"Cytokinetic bridge","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MAP2K5"},"hgnc":{"alias_symbol":["MEK5","MAPKK5","HsT17454"],"prev_symbol":["PRKMK5"]},"alphafold":{"accession":"Q13163","domains":[{"cath_id":"3.10.20.90","chopping":"16-108","consensus_level":"high","plddt":85.0494,"start":16,"end":108},{"cath_id":"3.30.200.20","chopping":"157-243","consensus_level":"medium","plddt":86.0823,"start":157,"end":243},{"cath_id":"1.10.510.10","chopping":"248-448","consensus_level":"medium","plddt":87.3719,"start":248,"end":448}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13163","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q13163-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q13163-F1-predicted_aligned_error_v6.png","plddt_mean":78.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MAP2K5","jax_strain_url":"https://www.jax.org/strain/search?query=MAP2K5"},"sequence":{"accession":"Q13163","fasta_url":"https://rest.uniprot.org/uniprotkb/Q13163.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q13163/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13163"}},"corpus_meta":[{"pmid":"11387209","id":"PMC_11387209","title":"Activated 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Alternative splicing produces a 50-kDa alpha isoform (expressed in liver and brain, particulate) and a 40-kDa beta isoform (ubiquitously distributed, primarily cytosolic), with differential subcellular localization determined by a 23-amino-acid N-terminal domain in MEK5α.\",\n      \"method\": \"PCR cloning, substrate phosphorylation assays in vitro, subcellular fractionation, tissue distribution analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original discovery with in vitro kinase assays and fractionation, foundational paper\",\n      \"pmids\": [\"7499418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"MEKK3 physically interacts with MEK5 (identified by yeast two-hybrid and confirmed by co-immunoprecipitation in mammalian cells), and a dominant-active MEKK3 stimulates BMK1/ERK5 activity through MEK5; MEKK3 kinase activity is required for growth-factor-mediated activation of endogenous BMK1.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, dominant-active/kinase-dead mutant expression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP and epistasis with kinase-dead mutants, replicated in multiple cell systems\",\n      \"pmids\": [\"10593883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The ERK5/MEK5 pathway is required for Raf-dependent cellular transformation; constitutively active MEK5 (MEK5DD) synergizes with Raf to transform NIH 3T3 cells. Endogenous Raf-1 binds specifically to endogenous ERK5 (not ERK2 or SAPK), and Raf-1 contributes to Ras activation of ERK5 through protein-protein interactions rather than catalytic activity.\",\n      \"method\": \"Co-immunoprecipitation, NIH 3T3 transformation assay, dominant-negative and constitutively active MEK5 mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis with defined mutants, transformation assay, reciprocal Co-IP\",\n      \"pmids\": [\"10531364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MEKK2 binds MEK5 via yeast two-hybrid and co-immunoprecipitation, activates BMK1/ERK5 through MEK5, and does so to a greater extent than MEKK3. A dominant-negative MEK5 specifically blocks MEKK2-induced BMK1/ERK5 activation without affecting JNK, establishing MEK5 as a specific downstream effector of MEKK2 in the BMK1/ERK5 pathway.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, dominant-negative MEK5, kinase assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP and epistasis confirmed with dominant-negative constructs\",\n      \"pmids\": [\"11073940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Constitutively active MEK5 in cardiomyocytes induces serial sarcomere assembly and an elongated hypertrophic morphology, and dominant-negative MEK5 specifically blocks LIF-induced elongation. Cardiac-specific expression of activated MEK5 in transgenic mice causes eccentric cardiac hypertrophy progressing to dilated cardiomyopathy and sudden death, establishing MEK5-ERK5 as the pathway mediating cytokine-induced serial sarcomere assembly.\",\n      \"method\": \"Adenoviral expression of CA/DN MEK5 in cardiomyocytes, transgenic mice, morphological analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean in vitro and in vivo loss/gain-of-function with specific phenotypic readout, replicated across models\",\n      \"pmids\": [\"11387209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Atypical protein kinase C isoforms (aPKCs, zetaPKC and lambda/iotaPKC) interact with MEK5 in an EGF-inducible manner, and this interaction is required and sufficient for MEK5 activation in response to EGF. aPKCs activate the Jun promoter through the MEF2C element (an ERK5 target) via MEK5.\",\n      \"method\": \"Co-immunoprecipitation, dominant-negative and constitutively active constructs, reporter assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and epistasis in a single study\",\n      \"pmids\": [\"11158308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The PB1 domains of MEKK2 and MEKK3 heterodimerize with the PB1 domain of MEK5 (but not with each other) both in vitro and in vivo. Deletion or mutation of the MEKK2 PB1 domain abolishes MEKK2-MEK5 complexes, and expression of the free MEKK2 or MEKK3 PB1 domain specifically inhibits ERK5 activation without affecting p38 or JNK pathways.\",\n      \"method\": \"In vitro PB1 domain binding, co-immunoprecipitation, mutagenesis, dominant-interference PB1 domain expression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of PB1-PB1 interaction, mutagenesis, and cell-based epistasis\",\n      \"pmids\": [\"12912994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Activation of the MEK5-ERK5 pathway causes phosphorylation and stabilization of c-Fos and Fra-1. ERK5 directly phosphorylates c-Fos at sites distinct from ERK1/2 phosphorylation sites, and the C-terminal half of ERK5 is necessary for maximal transactivation of c-Fos and Fra-1.\",\n      \"method\": \"Constitutively active MEK5, phosphorylation assays, transactivation reporter assays, truncation mutants of ERK5\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — kinase assays with mutagenesis and functional reporter readouts in single study\",\n      \"pmids\": [\"12622723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"MEK5 overexpression in prostate cancer cells stimulates proliferation, motility, and invasion, markedly increases MMP-9 (but not MMP-2) mRNA expression, and activates AP-1 (but not NF-κB) transcription via the MMP-9 promoter, establishing MEK5 as an upstream regulator of MMP-9/AP-1 in prostate cancer invasion.\",\n      \"method\": \"MEK5 transfection, luciferase reporter assays, EMSA, invasion assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays including EMSA and reporter assays in a single study\",\n      \"pmids\": [\"12618764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Endogenous MEK5 and ERK5 are localized predominantly in the nucleus in both resting and EGF-stimulated HeLa and Rat-1 cells, bound to detergent-resistant nuclear moieties, whereas their upstream activator MEKK2 is cytosolic at rest and translocates to the nucleus upon EGF stimulation.\",\n      \"method\": \"Immunofluorescence microscopy, in situ detergent extraction (NP-40), subcellular fractionation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiments with multiple methods (fractionation, extraction, imaging) in multiple cell lines\",\n      \"pmids\": [\"15075238\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The NMR structure of the PKCiota PB1 domain reveals it adopts a ubiquitin fold with an OPCA motif forming an acidic surface that mediates interaction with the basic surface of target PB1 domains including MEK5, confirmed by mutational analysis.\",\n      \"method\": \"NMR structure determination, mutational analysis of protein-protein interaction\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with functional validation by mutagenesis\",\n      \"pmids\": [\"15143057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CT-1-induced cardiac hypertrophy is mediated by the MEK5-ERK5 pathway: dominant-negative MEK5 suppresses CT-1-induced hypertrophy (protein synthesis, BNP secretion, cell surface area increase) while dominant-negative MEK1 does not, and CT-1 activates ERK5 phosphorylation that is blocked by SOCS1/3 overexpression.\",\n      \"method\": \"Adenoviral dominant-negative MEK5/MEK1, SOCS overexpression, phosphorylation assays, hypertrophy markers\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific epistasis with DN-MEK5 vs. DN-MEK1, multiple readouts\",\n      \"pmids\": [\"15623437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Targeted deletion of mek5 in mice results in embryonic lethality at ~E10.5 with abnormal cardiac development, decreased proliferation and increased apoptosis. In mek5-/- MEFs, MEK5 is required for ERK5 activation and for MEF2 transcriptional activity; MEK5 loss sensitizes cells to sorbitol-induced caspase-3 activation without affecting cell cycle progression.\",\n      \"method\": \"Knockout mice, MEF analysis, ERK5 kinase assays, caspase activity assays, MEF2 reporter assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — genetic knockout with multiple orthogonal mechanistic readouts in vivo and in vitro\",\n      \"pmids\": [\"15601854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The MEK5-ERK5 cascade is activated in biliary epithelial cells of polycystic kidney (PCK) rats, driving aberrant proliferation; siRNA knockdown of MEK5 significantly inhibits this hyperproliferation, while MEK1/2 inhibitors (PD98059, U0126) are less effective, establishing MEK5-ERK5 as the primary proliferative pathway in biliary dysgenesis.\",\n      \"method\": \"siRNA knockdown, kinase phosphorylation assays, proliferation assays, pharmacological inhibitors\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with pathway-specific pharmacological comparison\",\n      \"pmids\": [\"15631999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In Xenopus, MEK5-ERK5 is required for neural differentiation downstream of SoxD and upstream of Xngnr1 (a proneural gene); morpholino knockdown of ERK5 or MEK5 reduces head structure and inhibits neural differentiation, and forced MEK5-ERK5 activation alone is sufficient to induce neural differentiation.\",\n      \"method\": \"Morpholino antisense knockdown, constitutively active MEK5 expression, in vivo Xenopus assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis (loss-of-function + gain-of-function) with defined pathway position in vivo\",\n      \"pmids\": [\"16179948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"MEKK2 and MEK5 PB1 domains form a front-to-back heterodimer via basic (MEKK2) and acidic (MEK5) surfaces; a C-terminal 34-amino-acid extension of the MEK5 PB1 domain encodes an ERK5 docking site required for MEK5 activation of ERK5. MEKK2 in its quiescent state preferentially binds MEK5; upon activation, MEKK2 also binds MKK7 via the acidic cluster of its PB1 domain to activate JNK.\",\n      \"method\": \"Domain interaction mapping, mutagenesis, co-immunoprecipitation, kinase assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis and domain reconstitution defining molecular mechanism\",\n      \"pmids\": [\"17452462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"NMR solution structure of MEKK3 PB1 domain reveals a ubiquitin fold with cis/trans prolyl isomerization at Gln38-Pro39; MEKK3 PB1 binds MEK5 PB1 with Kd ~10^-8 M, with Lys7 and Arg5 of the basic cluster being critical for MEK5 PB1 interaction.\",\n      \"method\": \"NMR structure determination, backbone dynamics, mutagenesis, binding affinity measurement\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with mutagenesis defining binding mechanism\",\n      \"pmids\": [\"17985933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Constitutively active MEK5α inhibits ERK5 SUMOylation (at K6/K22) independently of its kinase activity but dependent on MEK5-ERK5 physical association, thereby preventing Ubc9/PIAS1-mediated SUMOylation that suppresses ERK5 transcriptional activity; H2O2 and high glucose induce ERK5 SUMOylation and reduce its transcriptional activity.\",\n      \"method\": \"CA-MEK5α transgenic mice, SUMOylation-site mutants (K6R/K22R), siRNA-PIAS1, DN-Ubc9, cardiac function assays\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis of SUMOylation sites, identification of writer (Ubc9/PIAS1), transgenic mouse validation\",\n      \"pmids\": [\"18467627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Pharmacological inhibitors BIX02188 and BIX02189 inhibit purified MEK5 enzymatic activity and selectively block ERK5 phosphorylation without affecting ERK1/2 phosphorylation in sorbitol-stimulated cells; they also inhibit MEF2C transcriptional activation downstream of MEK5/ERK5.\",\n      \"method\": \"In vitro kinase assay with purified MEK5, cell-based ERK5/ERK1/2 phosphorylation assays, MEF2C reporter assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified enzyme assay with selectivity demonstration in cells\",\n      \"pmids\": [\"18834865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MEK5-BMK1 (ERK5), but not MEK1-ERK1/2, mediates fluid shear stress inhibition of TNF-induced JNK activation in endothelial cells; selective MEK5 inhibitor BIX02188 completely reverses flow-mediated inhibition of JNK, while MEK1/2-selective concentrations of PD184352 have no effect.\",\n      \"method\": \"Pharmacological inhibitors at selective concentrations, shear stress apparatus, JNK activation assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway epistasis using selective inhibitors with defined mechanism\",\n      \"pmids\": [\"18358237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MEK5/ERK5 activation promotes an epithelial-to-mesenchymal transition (EMT) phenotype in breast cancer cells, with upregulation of vimentin, SNAI2 (slug), ZEB1, and N-cadherin, and downregulation of E-cadherin and keratins; shRNA targeting ERK5 reverses MEK5-mediated EMT gene expression.\",\n      \"method\": \"MEK5 overexpression, proteomics (2D-gel/LC-MS/MS), ERK5 shRNA knockdown, immunofluorescence\",\n      \"journal\": \"Breast cancer research : BCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (proteomics + shRNA rescue) in single study\",\n      \"pmids\": [\"19087274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MEK5-ERK5 regulates thymocyte apoptosis but not positive selection; retroviral dominant-negative MEK5 in developing thymocytes increases apoptosis while constitutively active MEK5 reduces it; ERK5 activity correlates with Nur77 family member levels (but not Bim) as effectors of thymocyte apoptosis.\",\n      \"method\": \"Retroviral expression of DN/CA MEK5 in thymocytes, apoptosis assays, Nur77/Bim expression analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function and loss-of-function with pathway effector identification\",\n      \"pmids\": [\"18548009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MEK5/ERK5 signaling downstream of VEGF induces Id1 and suppresses thrombospondin-1 (TSP1) expression to promote angiogenesis; Epac/Rap1 antagonizes this by suppressing Id1 and inducing TSP1, establishing MEK5 as a pro-angiogenic component controlling Id1/TSP1 balance.\",\n      \"method\": \"MEK5 knockdown/overexpression, TSP1 and Id1 expression assays, in vivo angiogenesis assay, Epac/Rap1 activation\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal experiments defining pathway position and effectors\",\n      \"pmids\": [\"19710505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Constitutive MEK5/ERK5 activation strongly inhibits endothelial cell migration and increases focal contact number and size via decreased expression of p130Cas (a key regulator of focal contact turnover); this results in increased cell rigidity and reduced motility.\",\n      \"method\": \"Retroviral CA-MEK5 expression, migration assays, focal contact imaging, p130Cas expression analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined molecular effector (p130Cas) with functional migration readout\",\n      \"pmids\": [\"19605361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MEK5 and ERK5 are required for the pro-myogenic actions of IGF-2; dominant-negative MEK5 blocks IGF-2-induced myogenesis and dominant-negative ERK5 prevents nuclear localization of ERK5-GFP upon MEK5 activation; constitutively active MEK5 rescues defects caused by antisense Igf2.\",\n      \"method\": \"CA/DN MEK5 expression, ERK5-GFP live imaging, kinase activity assays, myogenic reporter assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function rescue and loss-of-function with live imaging of ERK5 translocation\",\n      \"pmids\": [\"19654213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MEK5 is activated by laminar shear stress in human dermal microvascular endothelial cells, activates ERK5, and induces KLF4 expression (in an ERK5-dependent manner); MEK5/ERK5/KLF4 signaling reduces endothelial inflammatory responses to TNF, in part mediated by KLF4.\",\n      \"method\": \"Laminar shear stress, constitutively active MEK5 expression, siRNA knockdown of ERK5 and KLF4, Western blotting, microarray\",\n      \"journal\": \"Microcirculation (New York, N.Y. : 1994)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis with siRNA knockdown and CA mutants defining pathway order\",\n      \"pmids\": [\"21166929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"XIAP directly interacts with MEKK2/3 and competes with PB1 domain-mediated binding to MEK5. XIAP and cIAP1 conjugate predominantly K63-linked ubiquitin chains to MEKK2 and MEKK3, which directly impedes MEK5-ERK5 interaction in a trimeric complex, leading to ERK5 inactivation; loss of XIAP or cIAP1 causes ERK5 hyperactivation and promotes myoblast differentiation via MEKK2/3-ERK5.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, ubiquitin linkage analysis, XIAP/cIAP1 knockdown/knockout, myoblast differentiation assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted ubiquitination mechanism with defined linkage type, competition assay, and cellular phenotype validation\",\n      \"pmids\": [\"24975362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"miR-143 directly represses MAP2K5 mRNA, modulating MAP2K5-ERK5 signaling during adipogenic differentiation of adipose-derived stromal cells; the stage-specific effect of miR-143 on adipogenesis is dependent on MAP2K5 suppression.\",\n      \"method\": \"miRNA overexpression, luciferase reporter assay for direct targeting, knockdown/overexpression of MAP2K5\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct targeting confirmed by reporter assay with functional differentiation readout\",\n      \"pmids\": [\"24448661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"YAP promotes myogenic differentiation via MEK5-ERK5 by activating the Abl/Src/MEKK3/MEK5/ERK5 cascade; co-immunoprecipitation shows YAP interacts with MEKK3 and ERK5; site-directed mutagenesis of MEKK3 Y181F (disrupting the PPGY/YAP interaction motif) inhibits MEK5/ERK5 activation and myogenic differentiation.\",\n      \"method\": \"Co-immunoprecipitation, constitutively active MEK5 expression, site-directed mutagenesis, inhibitor studies, myogenic differentiation assays\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with mutagenesis defining interaction motif and functional consequence\",\n      \"pmids\": [\"28356344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MAP2K5 variants A321T and M367T (located in the kinase domain) consistently phosphorylate ERK5 at Ser731+Thr733 or Ser496, promoting ERK5 nuclear translocation and altering downstream gene expression, resulting in thyroid epithelial cell malignant transformation.\",\n      \"method\": \"Functional study of kinase domain variants, ERK5 phosphorylation assays, nuclear translocation assays, cell transformation assays\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional validation of specific kinase domain mutations with phosphorylation site identification\",\n      \"pmids\": [\"30132833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"KRAS suppression-induced MYC degradation is antagonized by an ERK1/2-inhibition-induced feedforward mechanism involving EGFR and SRC leading to ERK5 (via MEK5) activation and phosphorylation of MYC at S62, preventing its degradation; concurrent ERK1/2 and ERK5 inhibition causes synergistic MYC loss and PDAC growth suppression.\",\n      \"method\": \"Kinome-wide proteomics screen, high-throughput MYC degradation screen, ERK5/MEK5 inhibitors, phospho-MYC S62 assays, PDAC cell growth assays\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — identified specific phosphorylation site (S62) on MYC by MEK5-ERK5, validated by multiple screens and pharmacological approaches\",\n      \"pmids\": [\"30423298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Resistance to ERK inhibitors (SCH772984) and BRAF/MEK inhibitors in melanoma involves activation of the IGF1R-MEK5-ERK5 signaling pathway, which counteracts inhibition of ERK1/2 activation; IGF1R inhibition blocks ERK5 activation in resistant cells and reduces growth in 3D spheroids and in vivo.\",\n      \"method\": \"Drug-resistant cell line generation, ERK5/ERK1/2 phosphorylation assays, IGF1R inhibition, 3D spheroid assays, xenograft models\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined pathway (IGF1R→MEK5→ERK5) with pharmacological epistasis and in vivo validation\",\n      \"pmids\": [\"30833419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MEK5 knockdown in prostate cancer cells impairs phosphorylation of the catalytic subunit of DNA-PK at Ser2056 in response to ionizing radiation or etoposide, delays resolution of γH2AX and 53BP1 foci, and compromises nonhomologous end joining (NHEJ) repair, sensitizing cells to genotoxic stress.\",\n      \"method\": \"MEK5 siRNA knockdown, DNA-PK phosphorylation assays, γH2AX/53BP1 foci imaging, NHEJ cell-based assay, clonogenic survival, xenograft experiments\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including NHEJ assay, phosphorylation, foci dynamics, and in vivo validation\",\n      \"pmids\": [\"31980741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The MEK5-ERK5 axis controls lipid metabolism in small-cell lung cancer, including the mevalonate/cholesterol synthesis pathway; depletion of MEK5/ERK5 perturbs lipid metabolism pathways and sensitizes SCLC cells to statin treatment.\",\n      \"method\": \"MEK5/ERK5 knockdown, transcriptomics, lipidomics, pharmacological inhibition, in vitro and in vivo growth assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — transcriptomics and lipidomics with functional validation in vitro and in vivo\",\n      \"pmids\": [\"31969375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MEK5/ERK5 signaling mediates IL-4-induced M2 macrophage differentiation through regulation of c-Myc expression; ERK5 activation is required for M2 marker induction (Arg-1, Ym-1, Fizz-1) via c-Myc, independently of STAT3 or STAT6 phosphorylation, confirmed by myeloid-specific Erk5 knockout mice.\",\n      \"method\": \"MEK5 inhibitor, ERK5 inhibitor, myeloid-specific Erk5 conditional knockout (LysMcre/Erk5f/f), STAT3/6 phosphorylation assays, c-Myc expression analysis\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional knockout mouse model with pharmacological and genetic validation, pathway effector (c-Myc) identified\",\n      \"pmids\": [\"32745297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The MEKK3-MEK5-ERK5 kinase cascade is required for basal mitochondrial degradation (independent of exogenous damage); genetic or pharmacological inhibition of MEK5 or ERK5 increases mitochondrial content by reducing lysosome-mediated mitochondrial degradation, without affecting bulk autophagy, PINK1-Parkin mitophagy, or mitochondrial biogenesis.\",\n      \"method\": \"Genetic inhibition (CRISPR/knockout), pharmacological inhibitors, mitochondrial content quantification, lysosome-mediated degradation assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic and pharmacological approaches with specific mechanistic readouts distinguishing from other pathways\",\n      \"pmids\": [\"33101709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MEK5 inhibition in neuronal cells reduces p62 levels and increases LC3-II/LC3-I ratio (autophagy activation) in an mTOR- and ERK5-independent manner; MEK5 inhibition alleviates TDP-43 mislocalization and cell death in TDP-43-expressing neuronal cells, identifying MEK5 as a novel autophagy modulator.\",\n      \"method\": \"MEK5 inhibitor (BIX02188), autophagy markers (p62, LC3), mTOR assays, TDP-43 localization imaging\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological inhibition with multiple autophagy markers revealing ERK5-independent mechanism\",\n      \"pmids\": [\"31005259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The Hedgehog-GLI pathway regulates MEK5 and ERK5 expression in melanoma: GLI1 binds a non-canonical GLI consensus sequence at the MAPK7 (ERK5) promoter (confirmed by chromatin immunoprecipitation), and ERK5 is required for Hedgehog-GLI-dependent melanoma cell proliferation.\",\n      \"method\": \"Chromatin immunoprecipitation, GLI1 genetic inhibition (Patched-1 knockdown), ERK5 inhibition, proliferation assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP defining transcriptional regulation with functional epistasis\",\n      \"pmids\": [\"34681917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Map2k5 knockout mice display dopaminergic cell loss and decreased tyrosine hydroxylase in the nigrostriatal pathway, with behavioral phenotypes including decreased locomotion, coordination defects, and impaired prepulse inhibition, establishing MAP2K5 as a regulator of dopaminergic neuron survival in vivo.\",\n      \"method\": \"Targeted Map2k5 knockout mouse model, behavioral testing, immunohistochemistry for tyrosine hydroxylase\",\n      \"journal\": \"Frontiers in aging neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo knockout with specific neurochemical and behavioral phenotypes\",\n      \"pmids\": [\"34168549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MEK5-ERK5 activates the Hedgehog-GLI signaling pathway in melanoma: constitutively active MEK5 (MEK5DD) potentiates GLI transcriptional activity and increases GLI1/GLI2 protein levels; ERK5 silencing reduces GLI1/GLI2 mRNA and protein and inhibits GLI transcriptional activity; combined GLI and MEK5 inhibitors more effectively reduce melanoma spheroid growth.\",\n      \"method\": \"ERK5 shRNA, MEK5/ERK5 pharmacological inhibitors (JWG-071, AX15836, GW284543, BIX02189), MEK5DD overexpression, GLI luciferase reporter assay, 3D spheroid assays\",\n      \"journal\": \"Cellular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss-of-function with reporter assay defining pathway regulation\",\n      \"pmids\": [\"39998753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MAPKi/ERK5i co-inhibition in NRAS-mutant melanoma induces sustained G1 cell cycle arrest by suppressing Cyclin D1 and CDK4; forced expression of Cyclin D1 and CDK4 rescues cell cycle progression, identifying Cyclin D/CDK4 as the key mediators of the combined MEKi/ERK5i anti-proliferative effect.\",\n      \"method\": \"Transcriptome analysis, MEKi/ERK5i pharmacological inhibitors, Cyclin D1/CDK4 forced expression rescue, cell cycle analysis\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — rescue experiment with defined molecular effectors and transcriptome support\",\n      \"pmids\": [\"41053077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RBM39 (a splicing factor) maintains full-length MEK5 mRNA splicing; RBM39 knockdown causes mis-splicing of MEK5, generating aberrant isoforms with exon loss that lack kinase function and undergo proteasomal degradation, thereby inhibiting MM cell survival. Full-length MEK5 activity maintains MM cell survival via p65/NF-κB.\",\n      \"method\": \"RBM39 knockdown, indisulam-mediated RBM39 degradation, splicing analysis, MEK5 isoform characterization, proteasome inhibition, p65 activity assays\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined splicing-dependent regulation of MEK5 function with downstream effector identification\",\n      \"pmids\": [\"40048740\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAP2K5 (MEK5) is a dual-specificity MAP kinase kinase that functions as the obligate, specific activator of ERK5 (BMK1) within a three-tier cascade in which MEKK2 or MEKK3 (bound to MEK5 via PB1 domain heterodimerization) phosphorylate and activate MEK5, which in turn phosphorylates and activates ERK5; this pathway is activated by growth factors, cytokines, oxidative stress, and fluid shear stress to regulate cardiac sarcomere assembly, neural differentiation, thymocyte apoptosis, endothelial anti-inflammatory responses, M2 macrophage differentiation, basal mitochondrial degradation, myogenesis, and cell survival, with ERK5 activity subject to negative regulation by MEKK2/3 ubiquitination by XIAP/cIAP1 and by SUMOylation at K6/K22 (promoted by Ubc9/PIAS1 and antagonized by MEK5 association), while nuclear-localized MEK5 and ERK5 transmit signals to transcription factors including MEF2, c-Fos/Fra-1, KLF4, and NF-κB, and MEK5 also controls DNA repair (NHEJ via DNA-PK), lipid/cholesterol metabolism, MYC stability (via S62 phosphorylation by ERK5), and Hedgehog-GLI pathway activation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MAP2K5 (MEK5) is a dual-specificity MAP kinase kinase that serves as the obligate and specific activator of ERK5/BMK1, transducing signals from MEKK2/MEKK3 through PB1-domain-mediated heterodimerization to regulate cell survival, differentiation, cardiac development, and stress responses [PMID:7499418, PMID:12912994, PMID:15601854]. MEKK2 and MEKK3 bind MEK5 via front-to-back PB1 domain interactions (Kd ~10⁻⁸ M), with a C-terminal extension of the MEK5 PB1 domain encoding an ERK5 docking site essential for substrate activation; this cascade is negatively regulated by XIAP/cIAP1-mediated K63-linked ubiquitination of MEKK2/3, which disrupts the MEK5–ERK5 interaction [PMID:17452462, PMID:17985933, PMID:24975362]. MEK5-activated ERK5 phosphorylates transcription factors including MEF2C, c-Fos/Fra-1, and KLF4, and stabilizes MYC via S62 phosphorylation; MEK5 also promotes DNA-PK-dependent NHEJ repair, controls lipid/cholesterol metabolism, drives M2 macrophage differentiation through c-Myc, and maintains basal mitochondrial degradation [PMID:12622723, PMID:30423298, PMID:31980741, PMID:32745297, PMID:33101709, PMID:31969375]. Targeted deletion of Mek5 in mice causes embryonic lethality at ~E10.5 with cardiac defects, and Map2k5 knockout mice exhibit dopaminergic neuron loss with motor and sensorimotor gating deficits [PMID:15601854, PMID:34168549].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Identification of MEK5 as a novel MAP kinase kinase in a distinct signaling module resolved the question of whether additional MAPK cascades existed beyond the ERK1/2, JNK, and p38 pathways, revealing two splice isoforms (α and β) with distinct subcellular distributions.\",\n      \"evidence\": \"PCR cloning, in vitro substrate phosphorylation assays, and subcellular fractionation in multiple tissues\",\n      \"pmids\": [\"7499418\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The specific MAPK substrate of MEK5 was not yet identified\", \"No upstream kinase activating MEK5 was known\", \"Physiological roles were undefined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of MEKK3 and Raf-1 as upstream regulators of the MEK5–ERK5 cascade established the three-tier architecture of this pathway and its link to Ras-driven transformation.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, dominant-active/kinase-dead MEKK3 mutants, NIH 3T3 transformation assay with constitutively active MEK5\",\n      \"pmids\": [\"10593883\", \"10531364\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The molecular basis of MEKK3–MEK5 binding was unknown\", \"Whether MEKK2 also activates MEK5 was untested\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstration that MEKK2 binds and activates MEK5–ERK5 more potently than MEKK3 broadened the upstream input map and showed MEK5 is the specific mediator of MEKK2-to-ERK5 signaling.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, dominant-negative MEK5 selectively blocking MEKK2-induced ERK5 without affecting JNK\",\n      \"pmids\": [\"11073940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for MEKK2/3 selectivity for MEK5 over other MKKs was unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Constitutive MEK5 activation in cardiomyocytes induced serial sarcomere assembly and eccentric hypertrophy progressing to dilated cardiomyopathy in transgenic mice, establishing the first in vivo physiological role for MEK5–ERK5 signaling.\",\n      \"evidence\": \"Adenoviral CA/DN MEK5 in cardiomyocytes, cardiac-specific MEK5 transgenic mice with morphological and functional cardiac analysis\",\n      \"pmids\": [\"11387209\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous MEK5 is essential for cardiac development required loss-of-function genetics\", \"Downstream transcriptional effectors in the heart were not defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"PB1-domain-mediated heterodimerization was identified as the structural mechanism coupling MEKK2/3 to MEK5, with specificity encoded by complementary basic (MEKK2/3) and acidic (MEK5) surfaces on ubiquitin-fold PB1 domains.\",\n      \"evidence\": \"In vitro PB1 domain binding, co-immunoprecipitation, mutagenesis of PB1 domains, dominant-interference experiments, NMR structures\",\n      \"pmids\": [\"12912994\", \"15143057\", \"17985933\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length MEKK2/3–MEK5–ERK5 ternary complex structure was not resolved\", \"How PB1 domain interaction is regulated dynamically in cells was unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"MEK5–ERK5 was shown to regulate transcription factor outputs including c-Fos/Fra-1 stabilization and AP-1/MMP-9 transcription, connecting the pathway to gene expression programs for invasion and proliferation.\",\n      \"evidence\": \"CA-MEK5, phosphorylation assays, reporter assays, EMSA, invasion assays in prostate cancer cells\",\n      \"pmids\": [\"12622723\", \"12618764\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ERK5 phosphorylation sites on c-Fos were mapped but not confirmed by mass spectrometry\", \"Whether MEK5 regulates AP-1 independently of ERK5 was not addressed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Endogenous MEK5 and ERK5 were found to reside predominantly in the nucleus bound to detergent-resistant structures, revising the assumption that the cascade signals only from the cytoplasm.\",\n      \"evidence\": \"Immunofluorescence, in situ NP-40 extraction, subcellular fractionation in HeLa and Rat-1 cells\",\n      \"pmids\": [\"15075238\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nuclear substrates of MEK5 beyond ERK5 were not identified\", \"Whether nuclear MEK5 has kinase-independent scaffolding functions was untested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic knockout of Mek5 proved it is essential for embryonic viability and cardiac development, and demonstrated that MEK5 is the non-redundant upstream activator of ERK5 and MEF2 transcriptional activity, with a pro-survival role against stress-induced apoptosis.\",\n      \"evidence\": \"Mek5 knockout mice (lethal ~E10.5), MEF analysis of ERK5 activation, MEF2 reporter assays, caspase-3 activity assays\",\n      \"pmids\": [\"15601854\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conditional knockouts in specific tissues were not yet available\", \"Whether other kinases partially compensate in non-cardiac tissues was unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"MEK5–ERK5 was positioned as a key driver of neural differentiation downstream of SoxD in Xenopus, demonstrating conservation of its developmental signaling role across vertebrates.\",\n      \"evidence\": \"Morpholino knockdown of MEK5/ERK5 and constitutively active MEK5 in Xenopus embryos\",\n      \"pmids\": [\"16179948\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct phosphorylation targets of ERK5 in neural progenitors were not identified\", \"Whether MEK5 has mammalian neural differentiation roles was not yet shown in knockout models\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Detailed domain mapping revealed that a 34-amino-acid extension C-terminal to the MEK5 PB1 domain encodes the ERK5 docking site, and that MEKK2 switches between MEK5 and MKK7 binding upon activation, explaining how the PB1 module achieves pathway specificity.\",\n      \"evidence\": \"Domain interaction mapping, mutagenesis, co-immunoprecipitation, kinase assays\",\n      \"pmids\": [\"17452462\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure of the MEK5 PB1-ERK5 docking interaction was not solved\", \"How activation-dependent conformational change in MEKK2 triggers partner switching was not mechanistically defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"MEK5 was shown to antagonize ERK5 SUMOylation at K6/K22 through physical association (independently of its kinase activity), while BIX02188/BIX02189 were validated as selective MEK5 catalytic inhibitors, providing both a kinase-independent regulatory mechanism and pharmacological tools.\",\n      \"evidence\": \"SUMOylation-site mutants, siRNA-PIAS1, DN-Ubc9, transgenic mice; purified MEK5 in vitro kinase assays with BIX compounds, cell-based selectivity assays\",\n      \"pmids\": [\"18467627\", \"18834865\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SUMOylation-regulated ERK5 activity and kinase-dependent ERK5 activity converge on the same targets was unclear\", \"BIX compound selectivity against the full kinome was not comprehensively profiled\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"MEK5–ERK5 was identified as the pathway mediating flow-mediated inhibition of JNK in endothelial cells and as a driver of EMT in breast cancer, expanding its roles to vascular mechanotransduction and cancer metastasis.\",\n      \"evidence\": \"Selective MEK5 inhibitor BIX02188 in shear stress assays; MEK5 overexpression with proteomics and ERK5 shRNA in breast cancer cells\",\n      \"pmids\": [\"18358237\", \"19087274\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct endothelial substrates of ERK5 mediating JNK crosstalk were not identified\", \"EMT gene regulation by ERK5 was correlative without defined direct transcriptional targets\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"MEK5/ERK5 was shown to induce KLF4 in endothelial cells under shear stress, establishing a transcription factor link to anti-inflammatory vascular protection.\",\n      \"evidence\": \"Laminar shear stress, CA-MEK5, siRNA knockdown of ERK5 and KLF4 in dermal microvascular endothelial cells\",\n      \"pmids\": [\"21166929\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ERK5 directly phosphorylates KLF4 or acts through intermediate transcription factors was not determined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"XIAP/cIAP1-mediated K63-linked ubiquitination of MEKK2/3 was identified as a negative regulatory mechanism that disrupts the MEKK2/3–MEK5–ERK5 trimeric complex, adding an E3-ligase-based layer of pathway control relevant to myoblast differentiation.\",\n      \"evidence\": \"Ubiquitination assays with linkage analysis, competition binding experiments, XIAP/cIAP1 knockdown/knockout, myoblast differentiation assay\",\n      \"pmids\": [\"24975362\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other E3 ligases regulate the same complex was not tested\", \"Deubiquitinase(s) counteracting this modification were not identified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"MEK5–ERK5 was shown to stabilize MYC via ERK5-mediated S62 phosphorylation in PDAC, revealing a feedforward survival mechanism activated when ERK1/2 is inhibited.\",\n      \"evidence\": \"Kinome-wide proteomics, high-throughput MYC degradation screen, MEK5/ERK5 inhibitors, phospho-MYC S62 assays in PDAC cells\",\n      \"pmids\": [\"30423298\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this MEK5–ERK5–MYC axis operates in non-PDAC contexts was not established\", \"Direct ERK5-MYC phosphorylation was shown but in vitro kinase assay with purified components was not presented\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"MEK5 was found to promote DNA-PK Ser2056 phosphorylation and nonhomologous end joining (NHEJ) repair, revealing a role in the DNA damage response independent of its canonical ERK5 transcriptional outputs.\",\n      \"evidence\": \"MEK5 siRNA knockdown, DNA-PK phosphorylation assays, γH2AX/53BP1 foci kinetics, cell-based NHEJ assay, clonogenic survival, xenograft validation\",\n      \"pmids\": [\"31980741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MEK5 regulates DNA-PK directly or through ERK5 was not resolved\", \"The phosphorylation event linking MEK5 to DNA-PK Ser2056 was not reconstituted in vitro\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"MEK5–ERK5 was shown to control M2 macrophage differentiation via c-Myc (independent of STAT3/6) and to maintain basal mitochondrial degradation through lysosome-mediated turnover, expanding the pathway's roles to innate immunity and organelle homeostasis.\",\n      \"evidence\": \"Myeloid-specific Erk5 conditional knockout mice, MEK5/ERK5 inhibitors, CRISPR knockout, mitochondrial content quantification, lysosome degradation assays\",\n      \"pmids\": [\"32745297\", \"33101709\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The mitochondrial substrate or receptor targeted by ERK5 for lysosomal degradation was not identified\", \"Whether MEK5 has ERK5-independent roles in macrophage polarization was not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Map2k5 knockout mice showed dopaminergic neuron loss and motor/sensorimotor gating deficits, establishing an in vivo requirement for MEK5 in dopaminergic neuron survival and extending the pathway beyond developmental neurobiology to neurodegeneration-relevant phenotypes.\",\n      \"evidence\": \"Targeted Map2k5 knockout mouse model, behavioral testing, tyrosine hydroxylase immunohistochemistry\",\n      \"pmids\": [\"34168549\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of dopaminergic cell death (apoptosis vs. other) was not defined\", \"Whether ERK5 activation is reduced in these knockout brains was not directly shown\", \"Single study without independent replication\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"MEK5–ERK5 was shown to activate the Hedgehog-GLI pathway in melanoma and to cooperate with ERK1/2 to maintain Cyclin D1/CDK4 expression, while full-length MEK5 mRNA integrity was found to depend on the splicing factor RBM39 for NF-κB-mediated survival in myeloma.\",\n      \"evidence\": \"MEK5DD overexpression, ERK5 shRNA, GLI reporter assays, 3D spheroid assays; MEKi/ERK5i co-inhibition with Cyclin D1/CDK4 rescue; RBM39 knockdown/degradation with splicing analysis and p65 activity assays\",\n      \"pmids\": [\"39998753\", \"41053077\", \"40048740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ERK5 directly phosphorylates GLI1/2 was not established\", \"The exact mis-spliced MEK5 isoforms from RBM39 loss require further characterization\", \"Whether combined MEKi/ERK5i approaches have clinical efficacy is unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Critical mechanistic gaps remain: no high-resolution structure of a full-length MEKK2/3–MEK5–ERK5 ternary complex exists; the mechanism by which MEK5 regulates DNA-PK in NHEJ has not been reconstituted biochemically; the mitochondrial targets for MEK5–ERK5-dependent basal mitophagy are unknown; and the kinase-independent scaffolding functions of nuclear MEK5 are poorly characterized.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length ternary complex structure\", \"Biochemical reconstitution of MEK5-to-DNA-PK signaling\", \"Identity of mitochondrial degradation substrate/receptor\", \"Kinase-independent nuclear functions of MEK5\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 12, 18, 29]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 3, 6, 12, 15, 18]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [4, 12, 14]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [32]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [40]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [34]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [12, 21]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [33]}\n    ],\n    \"complexes\": [\n      \"MEKK2–MEK5–ERK5\",\n      \"MEKK3–MEK5–ERK5\"\n    ],\n    \"partners\": [\n      \"MAPK7\",\n      \"MAP3K2\",\n      \"MAP3K3\",\n      \"XIAP\",\n      \"BIRC2\",\n      \"PRKCZ\",\n      \"PRKCI\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}