{"gene":"MAP2K1","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2019,"finding":"Cryo-EM structures of full-length BRAF in complex with MEK1 and a 14-3-3 dimer revealed that in the autoinhibited state, MEK1 is held in an inactive BRAF-MEK1 complex restrained in a cradle formed by the 14-3-3 dimer binding phosphorylated S365 and S729 of BRAF. The 14-3-3 cradle maintains autoinhibition by sequestering the BRAF cysteine-rich domain and blocking BRAF kinase domain dimerization. In the active state, inhibitory interactions are released and a single 14-3-3 dimer bridges two BRAFs via C-terminal pS729 sites, driving formation of an active back-to-back BRAF dimer that activates MEK1.","method":"Cryo-electron microscopy of full-length protein complexes","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure of full-length BRAF-MEK1-14-3-3 complex in both autoinhibited and active states, multiple conformational snapshots with functional interpretation","pmids":["31581174"],"is_preprint":false},{"year":2009,"finding":"MEK1 forms a previously undiscovered heterodimer with MEK2. ERK-mediated phosphorylation of MEK1 at Thr292 (a residue absent in MEK2) negatively regulates the MEK1-MEK2 heterodimer, thereby downregulating MEK2-dependent ERK signaling. Loss of MEK1 (knockout embryos and mice) stabilizes phosphorylation of both MEK2 and ERK, demonstrating that MEK1 is the crucial modulator of MEK/ERK signaling duration and strength.","method":"Co-immunoprecipitation, MEK1 knockout mouse model, phosphosite mutagenesis, in vivo ERK/MEK phosphorylation assays","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP identifying novel heterodimer, confirmed in MEK1 KO mice and cultured cells, multiple orthogonal methods in one study","pmids":["19219045"],"is_preprint":false},{"year":1994,"finding":"MEK1 (MKK1) is negatively regulated by phosphorylation of Thr286 and Thr292 in vitro and in vivo. p34cdc2 catalyzes phosphorylation of both threonine residues and inactivates MEK1 enzymatic activity, providing a mechanism for cell-cycle-dependent downregulation of MEK1.","method":"In vitro kinase assay with p34cdc2, in vivo phosphorylation mapping, site-directed mutagenesis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with p34cdc2 plus in vivo phosphorylation confirmation, replicated and built upon in later studies","pmids":["8114697"],"is_preprint":false},{"year":2011,"finding":"MEK1 is activated by RAF-catalyzed phosphorylation of S218 and S222 in its activation segment. Phosphorylation of S212 in the activation segment is inhibitory. Active ERK catalyzes a feedback inhibitory phosphorylation of MEK1 at T292, serving to downregulate the pathway. The KSR scaffold is required both structurally and catalytically for MEK activation.","method":"Biochemical analysis, phosphosite mapping, review of kinase assay and mutagenesis data from multiple studies","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — synthesis of multiple experimental findings on activation/inhibitory phosphorylation; individual phosphosite results replicated across labs, but this specific paper is a review","pmids":["22177953"],"is_preprint":false},{"year":1999,"finding":"Nuclear localization of MEK1 is promoted by serum stimulation and by G2-M progression. Nuclear uptake requires phosphorylation (or negatively charged residues) at the activation lip (Ser218, Ser222) but not catalytic activity. Disruption of the MEK1 nuclear export signal (NES, residues 32–37) enhances nuclear accumulation. Signaling downstream of MEK (ERK activation) is also necessary for nuclear translocation.","method":"Fluorescence microscopy of NES-mutant and activation-site-mutant MEK1 constructs in transfected cells, pharmacological inhibitor (UO126) treatment, cell-cycle synchronization","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiments with multiple MEK1 mutants (NES, S218E/S222D, S218A/S222A, K97M) in cultured cells; single lab, several orthogonal perturbations","pmids":["10037701"],"is_preprint":false},{"year":2014,"finding":"H2S S-sulfhydrates MEK1 at Cys341, which activates ERK1/2 phosphorylation and promotes nuclear translocation of phospho-ERK1/2. Nuclear ERK1/2 then directly interacts with and activates PARP-1, which recruits XRCC1 and DNA ligase III to DNA breaks. Mutation of MEK1 Cys341 abolishes ERK phosphorylation and PARP-1 activation, linking H2S-induced MEK1 S-sulfhydration to DNA damage repair.","method":"S-sulfhydration assay, site-directed mutagenesis (C341), Co-IP of MEK1 with PARP-1, immunofluorescence of nuclear ERK, comet/DNA damage assays","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — novel PTM (S-sulfhydration) identified with mutagenesis and Co-IP; single lab, multiple orthogonal methods","pmids":["24778456"],"is_preprint":false},{"year":2021,"finding":"SIRT2 deacetylase downregulation increases acetylation of MEK1 at Lys175, resulting in ERK activation and subsequent activation of the pro-fission factor DRP1, linking SIRT2-MEK1-ERK-DRP1 axis to mitochondrial dynamics and somatic cell reprogramming (Warburg effect).","method":"Acetylation mass spectrometry, MEK1-K175 acetylation site identification, ERK and DRP1 phosphorylation assays upon SIRT2 knockdown/overexpression, mitochondrial morphology imaging","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — novel acetylation site identified by proteomics and validated functionally; single lab with multiple orthogonal readouts","pmids":["34965411"],"is_preprint":false},{"year":2021,"finding":"Arrestin-2 scaffolds the cRAF-MEK1-ERK2 signaling cascade. Basal and active arrestin-2 interact with cRAF, whereas only active arrestin-2 interacts with MEK1 and ERK2. The ATP-binding status of MEK1 affects arrestin-2 interaction: ATP-bound MEK1 interacts with arrestin-2, while only empty ERK2 binds arrestin-2. The relative positions of cRAF, MEK1, and ERK2 on arrestin-2 facilitate sequential phosphorylation.","method":"Hydrogen/deuterium exchange-mass spectrometry, tryptophan-induced bimane fluorescence quenching, NMR; binding interface mapping","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — three complementary structural/biophysical methods (HDX-MS, fluorescence quenching, NMR) in a single rigorous study defining binding interfaces","pmids":["34507982"],"is_preprint":false},{"year":2018,"finding":"Cancer-associated activating mutations in MEK1 fall into two mechanistic classes: (1) mutations that relieve inhibitory interactions with the helix A region (sensitive to traditional allosteric MEK inhibitors), and (2) in-frame deletions of the β3-αC loop that enhance MEK1 homodimerization, promoting intradimer cross-phosphorylation of the activation loop and conferring resistance to allosteric MEK inhibitors. MEK1 dimerization is required both for its activation by RAF and for its catalytic activity toward ERK.","method":"In vitro kinase assays, MEK1 dimerization assays, mutagenesis, in vivo tumor xenograft models, inhibitor sensitivity assays","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution of dimerization-dependent cross-phosphorylation, mutagenesis, and in vivo xenograft validation; multiple orthogonal methods in single study","pmids":["30377225"],"is_preprint":false},{"year":2022,"finding":"Molecular dynamics simulations clarified how B-Raf and KSR1 activate MEK1: the proline-rich (P-rich) loop of MEK1 plays a decisive role in MEK1 activation loop (A-loop) phosphorylation. In inactive B-Raf/MEK1 heterodimer, B-Raf's collapsed A-loop interacts with the P-rich loop and A-loop of MEK1 to minimize MEK1 A-loop fluctuation. In the active B-Raf/MEK1 heterodimer, P-rich loop movement reduces interactions with MEK1 A-loop, increasing flexibility and bringing Ser222 closer to ATP. B-Raf αG-helix Arg662 orients Ser218 toward ATP; KSR1 has Ala826 at the equivalent position, resulting in a more flexible MEK1 A-loop.","method":"Molecular dynamics simulations of B-Raf/MEK1 and KSR1/MEK1 complexes","journal":"Cellular and molecular life sciences : CMLS","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational (MD simulation) only, no in vitro or in vivo experimental validation in this paper","pmids":["35508574"],"is_preprint":false},{"year":2007,"finding":"WNK2 inhibits cell proliferation by negatively modulating MEK1 activity. WNK2 depletion activates ERK1/2 via MEK1 phosphorylation at Ser298, an effect that occurs downstream of Raf kinases. A kinase-dead WNK2-K207M mutant also activates ERK1/2, indicating WNK2 catalytic activity is required for suppression of the MEK1/ERK1/2 pathway.","method":"RNAi knockdown, kinase-dead mutant expression, Western blot for pMEK1(S298) and pERK1/2 in HeLa and HT29 cells","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi knockdown and kinase-dead mutant with defined phosphorylation readout; single lab, two orthogonal perturbations","pmids":["17667937"],"is_preprint":false},{"year":2015,"finding":"Polo-like kinase 1 (Plk1) controls MEK1/2 phosphorylation and ERK1/2 activation downstream of PDGF in airway smooth muscle cells. Plk1 knockdown attenuates PDGF-induced MEK1/2 and ERK1/2 phosphorylation without affecting Raf-1 or AKT phosphorylation. Expression of non-phosphorylatable T210A-Plk1 also inhibits MEK1/2 phosphorylation, indicating Plk1 kinase activity is required upstream of MEK1/2.","method":"Stable Plk1 knockdown cells, non-phosphorylatable Plk1 mutant (T210A), immunoblot for pMEK1/2 and pERK1/2","journal":"Respiratory research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, indirect evidence (KD + dominant-negative), no direct phosphorylation of MEK1 by Plk1 demonstrated in vitro","pmids":["26242183"],"is_preprint":false},{"year":2002,"finding":"MEKK1 ubiquitylation (via its PHD/E3 ligase domain) inhibits MEKK1's ability to phosphorylate MKK1 and MKK4, resulting in suppressed ERK1/2 and JNK activation. Mutation of Cys441 in the MEKK1 PHD domain blocks ubiquitylation and preserves MEKK1-catalyzed MKK1/MKK4 phosphorylation. MEKK1 kinase activity is required for its own ubiquitylation.","method":"In vitro kinase assay, ubiquitylation assay, site-directed mutagenesis (C441A), ERK1/2 and JNK activation assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro kinase and ubiquitylation assays with mutagenesis; single lab, demonstrates direct regulatory relationship between MEKK1 ubiquitylation and MKK1 phosphorylation","pmids":["12456688"],"is_preprint":false},{"year":2015,"finding":"MAP2K1 mutations identified in LCH (C121S, C121S/G128D, 56_61QKQKVG>R deletion) constitutively phosphorylate ERK in in vitro kinase assays. The C121S/G128D and 56_61QKQKVG>R variants were resistant to the MEK inhibitor trametinib in vitro, establishing that specific MAP2K1 mutations confer both constitutive ERK activation and MEK inhibitor resistance.","method":"In vitro kinase assay, trametinib resistance assay, targeted next-generation sequencing","journal":"Genes, chromosomes & cancer","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro kinase reconstitution for all three variants; single lab but direct enzymatic evidence","pmids":["25899310"],"is_preprint":false},{"year":2019,"finding":"MEK1 V211D gatekeeper mutation, acquired during clinical treatment with allosteric MEK inhibitor binimetinib, causes RAF-independent MEK1 activity, increases MEK1 catalytic activity, and reduces MEK1 affinity for binimetinib and all tested allosteric MEK inhibitors. V211D MEK1 remains regulated by RAF but is sensitive to ATP-competitive MEK inhibitors.","method":"Whole-genome sequencing of patient tumor, MEK1 kinase activity assays, drug-binding affinity assays, drug sensitivity assays in vitro and in vivo","journal":"Cancer discovery","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase and drug-affinity assays with clinical specimen validation; single lab, multiple orthogonal methods","pmids":["31227518"],"is_preprint":false},{"year":2004,"finding":"In transgenic murine and human epidermis, MEK1 (but not MEK2) recapitulated RAS/RAF effects—increasing proliferation, integrin expression, and suppressing differentiation. A kinase-dead MEK1 mutant incapable of phosphorylating ERK retained the ability to mediate MEK1-driven epidermal proliferation, indicating MEK1 promotes the proliferative epithelial phenotype partly through a kinase-independent mechanism.","method":"Transgenic mouse and human epidermal tissue models with inducible MEK1/MEK2 and kinase-dead MEK1 (K97R) constructs; ERK phosphorylation, proliferation, and differentiation assays","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic in vivo model with kinase-dead mutant to dissect kinase-dependent vs. independent functions; single lab","pmids":["15342384"],"is_preprint":false},{"year":1998,"finding":"Constitutively active MEK1 (fused to estrogen receptor hormone-binding domain) drives S-phase entry, proliferation in low serum, morphological transformation, and anchorage-independent growth in NIH-3T3 cells. Activated MEK1 induces upregulation of cyclin D1 and downregulation of p27(Kip1), establishing a direct link between MEK1 activity and cell cycle machinery.","method":"Inducible constitutively active MEK1-ER fusion in NIH-3T3 cells; cell cycle analysis, cyclin D1/p27 Western blots, transformation assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean inducible gain-of-function system with defined cell-cycle readouts; single lab","pmids":["9582373"],"is_preprint":false},{"year":2004,"finding":"MEK1 knockdown by RNAi leads to p21(cip1) induction and a senescence-like phenotype, and permanent MEK1 ablation reduces colony formation. In contrast, MEK2 deficiency induces cyclin D1 overexpression and CDK4/6 activation leading to nucleophosmin hyperphosphorylation and centrosome over-amplification. MEK1 and MEK2 thus differentially control the G1/S transition.","method":"RNA interference knockdown of MEK1 and MEK2 separately in human cells; cell cycle analysis, cyclin D1 and p21 immunoblots, colony formation assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — specific RNAi knockdown with distinct cell-cycle phenotypes for each isoform; single lab, multiple readouts","pmids":["15284233"],"is_preprint":false},{"year":2017,"finding":"Activating variants at MEK1 Phe53 are phosphorylated by RAF faster than wild-type MEK1 and show constitutive activity, but the maximal activities of fully phosphorylated wild-type and mutant enzymes are indistinguishable. The activating substitutions destabilize the inactive conformation of MEK1, increasing susceptibility to RAF-mediated phosphorylation. In zebrafish, developmental effects of activating variants reflect joint control by the negative regulatory region and activating phosphorylation.","method":"In vitro Raf phosphorylation kinetics assay, MEK1 kinase activity assay, zebrafish developmental assays with activating MEK1 variants","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with defined kinetics plus in vivo zebrafish validation; single lab, multiple orthogonal methods","pmids":["29018093"],"is_preprint":false},{"year":2015,"finding":"Cdk5 phosphorylates MEK1 only at Thr292, whereas ERK and Cdk1 phosphorylate both Thr292 and Thr286. Both sites interact in a kinase-specific manner to inhibit MEK1's ability to activate ERK. Thr292 phosphorylation is regulated by cAMP-dependent signaling in mouse striatum consistent with negative feedback inhibition following ERK activation. Protein phosphatase 1 and 2A contribute to basal phosphorylation at both sites.","method":"In vitro kinase assays with Cdk5, ERK, Cdk1 and MEK1; phosphosite mapping; immunoprecipitation from mouse brain tissue; pharmacological inhibitor studies","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assays with site mapping plus in vivo brain tissue phosphorylation analysis; single lab, multiple kinases tested","pmids":["25971971"],"is_preprint":false},{"year":2021,"finding":"MEK1 deletion (LysMCre × Mek1fl) in myeloid cells results in failure to resolve LPS-induced acute lung injury, with alveolar macrophages lacking MEK1 showing increased MEK2 and ERK1/2 activation on day 4 of injury, demonstrating that MEK1 specifically limits the duration of macrophage proinflammatory ERK signaling to promote resolution.","method":"Conditional Mek1 knockout mice (LysMCre), LPS-induced acute lung injury model, ERK1/2 and MEK2 phosphorylation assays in alveolar macrophages","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with specific cellular phenotype and defined signaling readout; single lab","pmids":["31801908"],"is_preprint":false},{"year":2016,"finding":"Genetic deletion of MEK1 in macrophages (LysMCre+/+Mek1fl/fl) significantly increases expression of IL-4/IL-13 (M2)-responsive genes and enhances macrophage efferocytosis of apoptotic cells, associated with increased expression of Mertk, Tyro3, and Abca1. MEK1 deletion-enhanced M2 polarization is dependent on STAT6 signaling (MEKi enhanced STAT6 phosphorylation), while enhanced efferocytosis is independent of polarization and STAT6.","method":"Conditional Mek1 KO (LysMCre), pharmacological MEKi, STAT6 knockout validation, in vivo peritoneal efferocytosis assay, LPS lung injury model","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic deletion complemented by pharmacological inhibition and epistasis with STAT6 KO; single lab, multiple orthogonal approaches","pmids":["28003382"],"is_preprint":false},{"year":2021,"finding":"MEK1 SUMOylation is enhanced by monensin treatment in ovarian cancer cells. Increased MEK1 SUMOylation correlates with suppression of the MEK-ERK pathway and inhibition of cell proliferation and invasion both in vitro and in xenograft models.","method":"SUMOylation assay in vitro and in vivo, xenograft tumor model, proliferation/invasion assays","journal":"Experimental and therapeutic medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, SUMOylation identification without mapping specific sites or identifying the SUMO E3 ligase; indirect correlative data","pmids":["34650638"],"is_preprint":false},{"year":2004,"finding":"Transgenic mice with cardiac-specific activated MEK1-ERK1/2 signaling are largely resistant to ischemia-reperfusion injury (reduced DNA laddering, TUNEL-positive cells, preserved hemodynamic function). Erk2+/- mice showed enhanced infarction and apoptosis, establishing that MEK1-ERK2 signaling is causally required for cardioprotection against ischemia-reperfusion injury.","method":"MEK1 cardiac transgenic mice, Erk1 null and Erk2 heterozygous knockout mice, ischemia-reperfusion model, TUNEL, DNA laddering, pressure-volume loops","journal":"Circulation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — complementary gain- and loss-of-function mouse models with defined cardioprotective phenotype; single lab, multiple orthogonal readouts","pmids":["15096454"],"is_preprint":false}],"current_model":"MAP2K1 (MEK1) is a dual-specificity kinase that phosphorylates ERK1/2 on Thr and Tyr residues after being activated by RAF-mediated phosphorylation of Ser218 and Ser222 in its activation loop; it is subject to multiple layers of regulation including: inhibitory phosphorylation at Thr286/Thr292 by p34cdc2, Cdk5, ERK (feedback), and Cdk1; S-sulfhydration at Cys341 that promotes nuclear ERK/PARP-1 signaling for DNA repair; acetylation at Lys175 regulated by SIRT2 that links MEK1 to mitochondrial dynamics; and SUMOylation that suppresses its activity. MEK1 physically interacts with BRAF and KSR1 (as shown by cryo-EM and MD simulations), forms a heterodimer with MEK2 whose stability is controlled by ERK-feedback phosphorylation of MEK1-Thr292, and is scaffolded with cRAF and ERK2 by arrestin-2. Activating mutations either relieve helix-A autoinhibition or enhance homodimerization to drive cross-phosphorylation of the activation loop; MEK1 is functionally distinct from MEK2 in promoting cell proliferation, controlling G1/S transition, and limiting the duration of macrophage inflammatory ERK signaling."},"narrative":{"mechanistic_narrative":"MAP2K1 (MEK1) is a dual-specificity protein kinase that occupies the central tier of the RAF-MEK-ERK cascade, transducing upstream RAF activity into ERK1/2 phosphorylation to control proliferation, cell-cycle progression, and tissue-specific signaling outcomes [PMID:30377225, PMID:9582373]. In the resting state MEK1 is held in an autoinhibited BRAF-MEK1 complex restrained by a 14-3-3 dimer; release of these inhibitory interactions permits a single 14-3-3 dimer to bridge two BRAF molecules into an active back-to-back dimer that activates MEK1 [PMID:31581174]. Activation proceeds through RAF-catalyzed phosphorylation of Ser218 and Ser222 in the activation segment, a step that also requires the KSR scaffold, while activated ERK imposes feedback inhibition by phosphorylating MEK1 at Thr292 [PMID:22177953]. MEK1 dimerization is itself required both for RAF-mediated activation and for catalytic activity toward ERK, and oncogenic mutations act either by relieving helix-A autoinhibition or by enhancing homodimerization to drive intradimer cross-phosphorylation, the latter conferring resistance to allosteric MEK inhibitors [PMID:30377225]. MEK1 is the dominant rheostat of pathway duration: it heterodimerizes with MEK2, and ERK-driven phosphorylation of the MEK1-specific Thr292 negatively regulates this heterodimer, such that loss of MEK1 stabilizes MEK2 and ERK phosphorylation [PMID:19219045]. Beyond catalysis, MEK1 activity is tuned by inhibitory phosphorylation at Thr286/Thr292 by p34cdc2, Cdk5, ERK, and Cdk1 [PMID:8114697, PMID:25971971], and by post-translational modifications including Cys341 S-sulfhydration that promotes nuclear ERK/PARP-1-dependent DNA repair [PMID:24778456] and Lys175 acetylation controlled by SIRT2 that links MEK1-ERK to DRP1-driven mitochondrial fission [PMID:34965411]. Functionally MEK1 is non-redundant with MEK2: it drives the G1/S transition through cyclin D1 induction and p27/p21 control [PMID:9582373, PMID:15284233], promotes epidermal proliferation in part through a kinase-independent mechanism [PMID:15342384], confers cardioprotection against ischemia-reperfusion injury via ERK2 [PMID:15096454], and limits the duration of macrophage proinflammatory ERK signaling to promote resolution of lung injury [PMID:31801908, PMID:28003382]. Recurrent activating MAP2K1 mutations cause constitutive ERK activation and MEK-inhibitor resistance in Langerhans cell histiocytosis and other cancers [PMID:25899310, PMID:31227518].","teleology":[{"year":1994,"claim":"Established that MEK1 is not only activated by upstream kinases but is also negatively controlled, defining a cell-cycle-linked inhibitory mechanism.","evidence":"In vitro kinase assay with p34cdc2 plus in vivo phosphorylation mapping and mutagenesis of Thr286/Thr292","pmids":["8114697"],"confidence":"High","gaps":["Did not resolve how inhibitory phosphorylation is reversed","Functional consequence for ERK output not quantified in this study"]},{"year":1998,"claim":"Demonstrated that MEK1 activity is sufficient to drive proliferation and transformation, linking the kinase directly to cell-cycle machinery.","evidence":"Inducible constitutively active MEK1-ER fusion in NIH-3T3 cells with cell-cycle, cyclin D1/p27, and transformation assays","pmids":["9582373"],"confidence":"Medium","gaps":["Whether endogenous MEK1 sets the same thresholds was untested","Does not distinguish MEK1 from MEK2 contributions"]},{"year":1999,"claim":"Showed that MEK1 subcellular distribution is regulated, addressing where MEK1 acts during the cell cycle.","evidence":"Fluorescence microscopy of NES- and activation-site-mutant MEK1 constructs with inhibitor and synchronization in cultured cells","pmids":["10037701"],"confidence":"Medium","gaps":["Nuclear substrates of MEK1 not identified","Single-lab localization study"]},{"year":2002,"claim":"Defined an upstream regulatory input by showing MEKK1 autoubiquitylation gates its ability to phosphorylate MKK1.","evidence":"In vitro kinase and ubiquitylation assays with MEKK1 PHD-domain mutagenesis","pmids":["12456688"],"confidence":"Medium","gaps":["Physiological contexts where MEKK1 controls MEK1 unclear","Did not map MEK1 phosphosites targeted by MEKK1"]},{"year":2004,"claim":"Resolved that MEK1 and MEK2 have non-redundant roles, with MEK1 specifically required to restrain G1/S progression and prevent senescence.","evidence":"Isoform-specific RNAi knockdown with cell-cycle, cyclin D1/p21, and colony-formation readouts; transgenic epidermal and cardiac models","pmids":["15284233","15342384","15096454"],"confidence":"Medium","gaps":["Molecular basis of MEK1 vs MEK2 substrate/output divergence not defined","Kinase-independent epidermal function mechanism unresolved"]},{"year":2007,"claim":"Identified WNK2 as an upstream negative regulator acting at the MEK1 level, expanding the network controlling pathway suppression.","evidence":"RNAi knockdown and kinase-dead WNK2 mutant with pMEK1(S298)/pERK readouts in HeLa and HT29 cells","pmids":["17667937"],"confidence":"Medium","gaps":["Whether WNK2 acts directly on MEK1 not shown","Mechanism connecting WNK2 to Ser298 phosphorylation unknown"]},{"year":2009,"claim":"Discovered the MEK1-MEK2 heterodimer and established MEK1 as the master modulator of pathway duration through Thr292 feedback.","evidence":"Reciprocal Co-IP, phosphosite mutagenesis, and MEK1 knockout mouse with in vivo ERK/MEK phosphorylation assays","pmids":["19219045"],"confidence":"High","gaps":["Structural geometry of the heterodimer not resolved","Quantitative contribution of heterodimer vs homodimer to ERK output unclear"]},{"year":2011,"claim":"Consolidated the activating and inhibitory phosphosite map and the KSR scaffold requirement into a coherent activation model.","evidence":"Synthesis of phosphosite mapping, kinase assay, and mutagenesis data (review)","pmids":["22177953"],"confidence":"Medium","gaps":["Review-level synthesis rather than new primary data","Dynamic interplay among phosphosites not quantified"]},{"year":2014,"claim":"Revealed a redox-sensing modification on MEK1 that couples H2S signaling to nuclear ERK-dependent DNA repair.","evidence":"S-sulfhydration assay, Cys341 mutagenesis, MEK1-PARP-1 Co-IP, nuclear ERK immunofluorescence, and DNA damage assays","pmids":["24778456"],"confidence":"Medium","gaps":["Single-lab finding without independent replication","Stoichiometry and physiological H2S thresholds undefined"]},{"year":2016,"claim":"Defined a tissue-specific MEK1 role in restraining macrophage M2 polarization and efferocytosis, separable from STAT6.","evidence":"Conditional Mek1 knockout, pharmacological MEKi, STAT6 KO epistasis, and in vivo efferocytosis and lung injury models","pmids":["28003382"],"confidence":"Medium","gaps":["MEK1 substrates governing efferocytosis genes not identified","STAT6-independent efferocytosis mechanism unresolved"]},{"year":2018,"claim":"Classified oncogenic MEK1 mutations by mechanism and established dimerization as essential for both activation and catalysis.","evidence":"In vitro kinase and dimerization assays, mutagenesis, inhibitor-sensitivity assays, and xenograft models","pmids":["30377225"],"confidence":"High","gaps":["Structural basis of homodimer cross-phosphorylation not directly visualized","In vivo prevalence of each mutation class not addressed"]},{"year":2019,"claim":"Provided the structural basis for MEK1 autoinhibition and activation within the 14-3-3-cradled BRAF complex.","evidence":"Cryo-EM of full-length BRAF-MEK1-14-3-3 complexes in autoinhibited and active states","pmids":["31581174"],"confidence":"High","gaps":["MEK1 catalytic transition state not captured","Role of MEK2 in analogous complexes not addressed"]},{"year":2019,"claim":"Characterized a clinically acquired gatekeeper mutation that uncouples MEK1 from allosteric inhibition while retaining ATP-competitive vulnerability.","evidence":"Whole-genome sequencing of patient tumor with MEK1 kinase, drug-affinity, and in vivo sensitivity assays for V211D","pmids":["31227518"],"confidence":"Medium","gaps":["Generality across other allosteric inhibitors beyond those tested","Resistance evolution dynamics in patients not tracked"]},{"year":2021,"claim":"Mapped how arrestin-2 scaffolds the cRAF-MEK1-ERK2 cascade and how MEK1 nucleotide state gates the interaction.","evidence":"HDX-MS, tryptophan-induced bimane fluorescence quenching, and NMR interface mapping","pmids":["34507982"],"confidence":"High","gaps":["Cellular consequences of scaffolded geometry not quantified","Whether MEK2 is similarly scaffolded unknown"]},{"year":2021,"claim":"Extended MEK1 regulation to acetylation, linking SIRT2-MEK1-ERK to DRP1-driven mitochondrial dynamics.","evidence":"Acetylation mass spectrometry, Lys175 site identification, and ERK/DRP1 phosphorylation with mitochondrial imaging upon SIRT2 perturbation","pmids":["34965411"],"confidence":"Medium","gaps":["Single-lab finding","Acetyltransferase opposing SIRT2 not identified"]},{"year":2021,"claim":"Demonstrated in vivo that MEK1 limits the duration of macrophage proinflammatory ERK signaling to enable resolution of lung injury.","evidence":"Conditional LysMCre Mek1 knockout in LPS-induced acute lung injury with macrophage MEK2/ERK phosphorylation readouts","pmids":["31801908"],"confidence":"Medium","gaps":["Mechanistic link between MEK1 loss and failed resolution incompletely defined","Relative roles of MEK2 derepression vs direct MEK1 loss unclear"]},{"year":2021,"claim":"Proposed SUMOylation as an additional negative regulatory modification of MEK1.","evidence":"SUMOylation assays and proliferation/invasion readouts in ovarian cancer cells and xenografts after monensin treatment","pmids":["34650638"],"confidence":"Low","gaps":["SUMO acceptor sites and responsible E3 ligase not identified","Correlative rather than direct causal evidence"]},{"year":2022,"claim":"Offered an atomistic rationale for how BRAF versus KSR1 differentially position the MEK1 activation loop for phosphorylation.","evidence":"Molecular dynamics simulations of B-Raf/MEK1 and KSR1/MEK1 heterodimers","pmids":["35508574"],"confidence":"Low","gaps":["Computational only, no experimental validation in this study","Predicted P-rich loop role not tested by mutagenesis"]},{"year":null,"claim":"How the many regulatory inputs on MEK1 — activating and inhibitory phosphorylation, S-sulfhydration, acetylation, SUMOylation, dimerization state, and scaffold occupancy — are integrated dynamically to set ERK signal amplitude and duration in a given cell type remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified quantitative model integrating MEK1 PTMs and dimerization","Cell-type-specific weighting of regulatory inputs undefined","Structural state of catalytically active MEK1 toward ERK not captured"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3,8,13,18]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[3,8,13]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[7]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,3,8]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[2,16,17]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[13,14,8]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[20,21]}],"complexes":["BRAF-MEK1-14-3-3 complex","MEK1-MEK2 heterodimer","cRAF-MEK1-ERK2 arrestin-2 scaffold complex"],"partners":["BRAF","KSR1","MAP2K2","MAPK1","RAF1","ARRB1","PARP1","SIRT2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q02750","full_name":"Dual specificity mitogen-activated protein kinase kinase 1","aliases":["ERK activator kinase 1","MAPK/ERK kinase 1","MEK 1"],"length_aa":393,"mass_kda":43.4,"function":"Dual specificity protein kinase which acts as an essential component of the MAP kinase signal transduction pathway. 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Part A","url":"https://pubmed.ncbi.nlm.nih.gov/27862862","citation_count":15,"is_preprint":false},{"pmid":"31827134","id":"PMC_31827134","title":"MAP2K1 is a potential therapeutic target in erlotinib resistant head and neck squamous cell carcinoma.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31827134","citation_count":15,"is_preprint":false},{"pmid":"34046359","id":"PMC_34046359","title":"Recurrent Somatic MAP2K1 Mutations in Papillary Thyroid Cancer and Colorectal Cancer.","date":"2021","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/34046359","citation_count":15,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":49580,"output_tokens":7035,"usd":0.127133,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":16082,"output_tokens":5483,"usd":0.108743,"stage2_stop_reason":"end_turn"},"total_usd":0.235876,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2019,\n      \"finding\": \"Cryo-EM structures of full-length BRAF in complex with MEK1 and a 14-3-3 dimer revealed that in the autoinhibited state, MEK1 is held in an inactive BRAF-MEK1 complex restrained in a cradle formed by the 14-3-3 dimer binding phosphorylated S365 and S729 of BRAF. The 14-3-3 cradle maintains autoinhibition by sequestering the BRAF cysteine-rich domain and blocking BRAF kinase domain dimerization. In the active state, inhibitory interactions are released and a single 14-3-3 dimer bridges two BRAFs via C-terminal pS729 sites, driving formation of an active back-to-back BRAF dimer that activates MEK1.\",\n      \"method\": \"Cryo-electron microscopy of full-length protein complexes\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure of full-length BRAF-MEK1-14-3-3 complex in both autoinhibited and active states, multiple conformational snapshots with functional interpretation\",\n      \"pmids\": [\"31581174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MEK1 forms a previously undiscovered heterodimer with MEK2. ERK-mediated phosphorylation of MEK1 at Thr292 (a residue absent in MEK2) negatively regulates the MEK1-MEK2 heterodimer, thereby downregulating MEK2-dependent ERK signaling. Loss of MEK1 (knockout embryos and mice) stabilizes phosphorylation of both MEK2 and ERK, demonstrating that MEK1 is the crucial modulator of MEK/ERK signaling duration and strength.\",\n      \"method\": \"Co-immunoprecipitation, MEK1 knockout mouse model, phosphosite mutagenesis, in vivo ERK/MEK phosphorylation assays\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP identifying novel heterodimer, confirmed in MEK1 KO mice and cultured cells, multiple orthogonal methods in one study\",\n      \"pmids\": [\"19219045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"MEK1 (MKK1) is negatively regulated by phosphorylation of Thr286 and Thr292 in vitro and in vivo. p34cdc2 catalyzes phosphorylation of both threonine residues and inactivates MEK1 enzymatic activity, providing a mechanism for cell-cycle-dependent downregulation of MEK1.\",\n      \"method\": \"In vitro kinase assay with p34cdc2, in vivo phosphorylation mapping, site-directed mutagenesis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with p34cdc2 plus in vivo phosphorylation confirmation, replicated and built upon in later studies\",\n      \"pmids\": [\"8114697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MEK1 is activated by RAF-catalyzed phosphorylation of S218 and S222 in its activation segment. Phosphorylation of S212 in the activation segment is inhibitory. Active ERK catalyzes a feedback inhibitory phosphorylation of MEK1 at T292, serving to downregulate the pathway. The KSR scaffold is required both structurally and catalytically for MEK activation.\",\n      \"method\": \"Biochemical analysis, phosphosite mapping, review of kinase assay and mutagenesis data from multiple studies\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — synthesis of multiple experimental findings on activation/inhibitory phosphorylation; individual phosphosite results replicated across labs, but this specific paper is a review\",\n      \"pmids\": [\"22177953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Nuclear localization of MEK1 is promoted by serum stimulation and by G2-M progression. Nuclear uptake requires phosphorylation (or negatively charged residues) at the activation lip (Ser218, Ser222) but not catalytic activity. Disruption of the MEK1 nuclear export signal (NES, residues 32–37) enhances nuclear accumulation. Signaling downstream of MEK (ERK activation) is also necessary for nuclear translocation.\",\n      \"method\": \"Fluorescence microscopy of NES-mutant and activation-site-mutant MEK1 constructs in transfected cells, pharmacological inhibitor (UO126) treatment, cell-cycle synchronization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiments with multiple MEK1 mutants (NES, S218E/S222D, S218A/S222A, K97M) in cultured cells; single lab, several orthogonal perturbations\",\n      \"pmids\": [\"10037701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"H2S S-sulfhydrates MEK1 at Cys341, which activates ERK1/2 phosphorylation and promotes nuclear translocation of phospho-ERK1/2. Nuclear ERK1/2 then directly interacts with and activates PARP-1, which recruits XRCC1 and DNA ligase III to DNA breaks. Mutation of MEK1 Cys341 abolishes ERK phosphorylation and PARP-1 activation, linking H2S-induced MEK1 S-sulfhydration to DNA damage repair.\",\n      \"method\": \"S-sulfhydration assay, site-directed mutagenesis (C341), Co-IP of MEK1 with PARP-1, immunofluorescence of nuclear ERK, comet/DNA damage assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — novel PTM (S-sulfhydration) identified with mutagenesis and Co-IP; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"24778456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIRT2 deacetylase downregulation increases acetylation of MEK1 at Lys175, resulting in ERK activation and subsequent activation of the pro-fission factor DRP1, linking SIRT2-MEK1-ERK-DRP1 axis to mitochondrial dynamics and somatic cell reprogramming (Warburg effect).\",\n      \"method\": \"Acetylation mass spectrometry, MEK1-K175 acetylation site identification, ERK and DRP1 phosphorylation assays upon SIRT2 knockdown/overexpression, mitochondrial morphology imaging\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — novel acetylation site identified by proteomics and validated functionally; single lab with multiple orthogonal readouts\",\n      \"pmids\": [\"34965411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Arrestin-2 scaffolds the cRAF-MEK1-ERK2 signaling cascade. Basal and active arrestin-2 interact with cRAF, whereas only active arrestin-2 interacts with MEK1 and ERK2. The ATP-binding status of MEK1 affects arrestin-2 interaction: ATP-bound MEK1 interacts with arrestin-2, while only empty ERK2 binds arrestin-2. The relative positions of cRAF, MEK1, and ERK2 on arrestin-2 facilitate sequential phosphorylation.\",\n      \"method\": \"Hydrogen/deuterium exchange-mass spectrometry, tryptophan-induced bimane fluorescence quenching, NMR; binding interface mapping\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — three complementary structural/biophysical methods (HDX-MS, fluorescence quenching, NMR) in a single rigorous study defining binding interfaces\",\n      \"pmids\": [\"34507982\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Cancer-associated activating mutations in MEK1 fall into two mechanistic classes: (1) mutations that relieve inhibitory interactions with the helix A region (sensitive to traditional allosteric MEK inhibitors), and (2) in-frame deletions of the β3-αC loop that enhance MEK1 homodimerization, promoting intradimer cross-phosphorylation of the activation loop and conferring resistance to allosteric MEK inhibitors. MEK1 dimerization is required both for its activation by RAF and for its catalytic activity toward ERK.\",\n      \"method\": \"In vitro kinase assays, MEK1 dimerization assays, mutagenesis, in vivo tumor xenograft models, inhibitor sensitivity assays\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution of dimerization-dependent cross-phosphorylation, mutagenesis, and in vivo xenograft validation; multiple orthogonal methods in single study\",\n      \"pmids\": [\"30377225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Molecular dynamics simulations clarified how B-Raf and KSR1 activate MEK1: the proline-rich (P-rich) loop of MEK1 plays a decisive role in MEK1 activation loop (A-loop) phosphorylation. In inactive B-Raf/MEK1 heterodimer, B-Raf's collapsed A-loop interacts with the P-rich loop and A-loop of MEK1 to minimize MEK1 A-loop fluctuation. In the active B-Raf/MEK1 heterodimer, P-rich loop movement reduces interactions with MEK1 A-loop, increasing flexibility and bringing Ser222 closer to ATP. B-Raf αG-helix Arg662 orients Ser218 toward ATP; KSR1 has Ala826 at the equivalent position, resulting in a more flexible MEK1 A-loop.\",\n      \"method\": \"Molecular dynamics simulations of B-Raf/MEK1 and KSR1/MEK1 complexes\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational (MD simulation) only, no in vitro or in vivo experimental validation in this paper\",\n      \"pmids\": [\"35508574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"WNK2 inhibits cell proliferation by negatively modulating MEK1 activity. WNK2 depletion activates ERK1/2 via MEK1 phosphorylation at Ser298, an effect that occurs downstream of Raf kinases. A kinase-dead WNK2-K207M mutant also activates ERK1/2, indicating WNK2 catalytic activity is required for suppression of the MEK1/ERK1/2 pathway.\",\n      \"method\": \"RNAi knockdown, kinase-dead mutant expression, Western blot for pMEK1(S298) and pERK1/2 in HeLa and HT29 cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi knockdown and kinase-dead mutant with defined phosphorylation readout; single lab, two orthogonal perturbations\",\n      \"pmids\": [\"17667937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Polo-like kinase 1 (Plk1) controls MEK1/2 phosphorylation and ERK1/2 activation downstream of PDGF in airway smooth muscle cells. Plk1 knockdown attenuates PDGF-induced MEK1/2 and ERK1/2 phosphorylation without affecting Raf-1 or AKT phosphorylation. Expression of non-phosphorylatable T210A-Plk1 also inhibits MEK1/2 phosphorylation, indicating Plk1 kinase activity is required upstream of MEK1/2.\",\n      \"method\": \"Stable Plk1 knockdown cells, non-phosphorylatable Plk1 mutant (T210A), immunoblot for pMEK1/2 and pERK1/2\",\n      \"journal\": \"Respiratory research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, indirect evidence (KD + dominant-negative), no direct phosphorylation of MEK1 by Plk1 demonstrated in vitro\",\n      \"pmids\": [\"26242183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"MEKK1 ubiquitylation (via its PHD/E3 ligase domain) inhibits MEKK1's ability to phosphorylate MKK1 and MKK4, resulting in suppressed ERK1/2 and JNK activation. Mutation of Cys441 in the MEKK1 PHD domain blocks ubiquitylation and preserves MEKK1-catalyzed MKK1/MKK4 phosphorylation. MEKK1 kinase activity is required for its own ubiquitylation.\",\n      \"method\": \"In vitro kinase assay, ubiquitylation assay, site-directed mutagenesis (C441A), ERK1/2 and JNK activation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase and ubiquitylation assays with mutagenesis; single lab, demonstrates direct regulatory relationship between MEKK1 ubiquitylation and MKK1 phosphorylation\",\n      \"pmids\": [\"12456688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MAP2K1 mutations identified in LCH (C121S, C121S/G128D, 56_61QKQKVG>R deletion) constitutively phosphorylate ERK in in vitro kinase assays. The C121S/G128D and 56_61QKQKVG>R variants were resistant to the MEK inhibitor trametinib in vitro, establishing that specific MAP2K1 mutations confer both constitutive ERK activation and MEK inhibitor resistance.\",\n      \"method\": \"In vitro kinase assay, trametinib resistance assay, targeted next-generation sequencing\",\n      \"journal\": \"Genes, chromosomes & cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase reconstitution for all three variants; single lab but direct enzymatic evidence\",\n      \"pmids\": [\"25899310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MEK1 V211D gatekeeper mutation, acquired during clinical treatment with allosteric MEK inhibitor binimetinib, causes RAF-independent MEK1 activity, increases MEK1 catalytic activity, and reduces MEK1 affinity for binimetinib and all tested allosteric MEK inhibitors. V211D MEK1 remains regulated by RAF but is sensitive to ATP-competitive MEK inhibitors.\",\n      \"method\": \"Whole-genome sequencing of patient tumor, MEK1 kinase activity assays, drug-binding affinity assays, drug sensitivity assays in vitro and in vivo\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase and drug-affinity assays with clinical specimen validation; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"31227518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In transgenic murine and human epidermis, MEK1 (but not MEK2) recapitulated RAS/RAF effects—increasing proliferation, integrin expression, and suppressing differentiation. A kinase-dead MEK1 mutant incapable of phosphorylating ERK retained the ability to mediate MEK1-driven epidermal proliferation, indicating MEK1 promotes the proliferative epithelial phenotype partly through a kinase-independent mechanism.\",\n      \"method\": \"Transgenic mouse and human epidermal tissue models with inducible MEK1/MEK2 and kinase-dead MEK1 (K97R) constructs; ERK phosphorylation, proliferation, and differentiation assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic in vivo model with kinase-dead mutant to dissect kinase-dependent vs. independent functions; single lab\",\n      \"pmids\": [\"15342384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Constitutively active MEK1 (fused to estrogen receptor hormone-binding domain) drives S-phase entry, proliferation in low serum, morphological transformation, and anchorage-independent growth in NIH-3T3 cells. Activated MEK1 induces upregulation of cyclin D1 and downregulation of p27(Kip1), establishing a direct link between MEK1 activity and cell cycle machinery.\",\n      \"method\": \"Inducible constitutively active MEK1-ER fusion in NIH-3T3 cells; cell cycle analysis, cyclin D1/p27 Western blots, transformation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean inducible gain-of-function system with defined cell-cycle readouts; single lab\",\n      \"pmids\": [\"9582373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"MEK1 knockdown by RNAi leads to p21(cip1) induction and a senescence-like phenotype, and permanent MEK1 ablation reduces colony formation. In contrast, MEK2 deficiency induces cyclin D1 overexpression and CDK4/6 activation leading to nucleophosmin hyperphosphorylation and centrosome over-amplification. MEK1 and MEK2 thus differentially control the G1/S transition.\",\n      \"method\": \"RNA interference knockdown of MEK1 and MEK2 separately in human cells; cell cycle analysis, cyclin D1 and p21 immunoblots, colony formation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — specific RNAi knockdown with distinct cell-cycle phenotypes for each isoform; single lab, multiple readouts\",\n      \"pmids\": [\"15284233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Activating variants at MEK1 Phe53 are phosphorylated by RAF faster than wild-type MEK1 and show constitutive activity, but the maximal activities of fully phosphorylated wild-type and mutant enzymes are indistinguishable. The activating substitutions destabilize the inactive conformation of MEK1, increasing susceptibility to RAF-mediated phosphorylation. In zebrafish, developmental effects of activating variants reflect joint control by the negative regulatory region and activating phosphorylation.\",\n      \"method\": \"In vitro Raf phosphorylation kinetics assay, MEK1 kinase activity assay, zebrafish developmental assays with activating MEK1 variants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with defined kinetics plus in vivo zebrafish validation; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"29018093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Cdk5 phosphorylates MEK1 only at Thr292, whereas ERK and Cdk1 phosphorylate both Thr292 and Thr286. Both sites interact in a kinase-specific manner to inhibit MEK1's ability to activate ERK. Thr292 phosphorylation is regulated by cAMP-dependent signaling in mouse striatum consistent with negative feedback inhibition following ERK activation. Protein phosphatase 1 and 2A contribute to basal phosphorylation at both sites.\",\n      \"method\": \"In vitro kinase assays with Cdk5, ERK, Cdk1 and MEK1; phosphosite mapping; immunoprecipitation from mouse brain tissue; pharmacological inhibitor studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assays with site mapping plus in vivo brain tissue phosphorylation analysis; single lab, multiple kinases tested\",\n      \"pmids\": [\"25971971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MEK1 deletion (LysMCre × Mek1fl) in myeloid cells results in failure to resolve LPS-induced acute lung injury, with alveolar macrophages lacking MEK1 showing increased MEK2 and ERK1/2 activation on day 4 of injury, demonstrating that MEK1 specifically limits the duration of macrophage proinflammatory ERK signaling to promote resolution.\",\n      \"method\": \"Conditional Mek1 knockout mice (LysMCre), LPS-induced acute lung injury model, ERK1/2 and MEK2 phosphorylation assays in alveolar macrophages\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with specific cellular phenotype and defined signaling readout; single lab\",\n      \"pmids\": [\"31801908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Genetic deletion of MEK1 in macrophages (LysMCre+/+Mek1fl/fl) significantly increases expression of IL-4/IL-13 (M2)-responsive genes and enhances macrophage efferocytosis of apoptotic cells, associated with increased expression of Mertk, Tyro3, and Abca1. MEK1 deletion-enhanced M2 polarization is dependent on STAT6 signaling (MEKi enhanced STAT6 phosphorylation), while enhanced efferocytosis is independent of polarization and STAT6.\",\n      \"method\": \"Conditional Mek1 KO (LysMCre), pharmacological MEKi, STAT6 knockout validation, in vivo peritoneal efferocytosis assay, LPS lung injury model\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic deletion complemented by pharmacological inhibition and epistasis with STAT6 KO; single lab, multiple orthogonal approaches\",\n      \"pmids\": [\"28003382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MEK1 SUMOylation is enhanced by monensin treatment in ovarian cancer cells. Increased MEK1 SUMOylation correlates with suppression of the MEK-ERK pathway and inhibition of cell proliferation and invasion both in vitro and in xenograft models.\",\n      \"method\": \"SUMOylation assay in vitro and in vivo, xenograft tumor model, proliferation/invasion assays\",\n      \"journal\": \"Experimental and therapeutic medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, SUMOylation identification without mapping specific sites or identifying the SUMO E3 ligase; indirect correlative data\",\n      \"pmids\": [\"34650638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Transgenic mice with cardiac-specific activated MEK1-ERK1/2 signaling are largely resistant to ischemia-reperfusion injury (reduced DNA laddering, TUNEL-positive cells, preserved hemodynamic function). Erk2+/- mice showed enhanced infarction and apoptosis, establishing that MEK1-ERK2 signaling is causally required for cardioprotection against ischemia-reperfusion injury.\",\n      \"method\": \"MEK1 cardiac transgenic mice, Erk1 null and Erk2 heterozygous knockout mice, ischemia-reperfusion model, TUNEL, DNA laddering, pressure-volume loops\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — complementary gain- and loss-of-function mouse models with defined cardioprotective phenotype; single lab, multiple orthogonal readouts\",\n      \"pmids\": [\"15096454\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAP2K1 (MEK1) is a dual-specificity kinase that phosphorylates ERK1/2 on Thr and Tyr residues after being activated by RAF-mediated phosphorylation of Ser218 and Ser222 in its activation loop; it is subject to multiple layers of regulation including: inhibitory phosphorylation at Thr286/Thr292 by p34cdc2, Cdk5, ERK (feedback), and Cdk1; S-sulfhydration at Cys341 that promotes nuclear ERK/PARP-1 signaling for DNA repair; acetylation at Lys175 regulated by SIRT2 that links MEK1 to mitochondrial dynamics; and SUMOylation that suppresses its activity. MEK1 physically interacts with BRAF and KSR1 (as shown by cryo-EM and MD simulations), forms a heterodimer with MEK2 whose stability is controlled by ERK-feedback phosphorylation of MEK1-Thr292, and is scaffolded with cRAF and ERK2 by arrestin-2. Activating mutations either relieve helix-A autoinhibition or enhance homodimerization to drive cross-phosphorylation of the activation loop; MEK1 is functionally distinct from MEK2 in promoting cell proliferation, controlling G1/S transition, and limiting the duration of macrophage inflammatory ERK signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAP2K1 (MEK1) is a dual-specificity protein kinase that occupies the central tier of the RAF-MEK-ERK cascade, transducing upstream RAF activity into ERK1/2 phosphorylation to control proliferation, cell-cycle progression, and tissue-specific signaling outcomes [#8, #16]. In the resting state MEK1 is held in an autoinhibited BRAF-MEK1 complex restrained by a 14-3-3 dimer; release of these inhibitory interactions permits a single 14-3-3 dimer to bridge two BRAF molecules into an active back-to-back dimer that activates MEK1 [#0]. Activation proceeds through RAF-catalyzed phosphorylation of Ser218 and Ser222 in the activation segment, a step that also requires the KSR scaffold, while activated ERK imposes feedback inhibition by phosphorylating MEK1 at Thr292 [#3]. MEK1 dimerization is itself required both for RAF-mediated activation and for catalytic activity toward ERK, and oncogenic mutations act either by relieving helix-A autoinhibition or by enhancing homodimerization to drive intradimer cross-phosphorylation, the latter conferring resistance to allosteric MEK inhibitors [#8]. MEK1 is the dominant rheostat of pathway duration: it heterodimerizes with MEK2, and ERK-driven phosphorylation of the MEK1-specific Thr292 negatively regulates this heterodimer, such that loss of MEK1 stabilizes MEK2 and ERK phosphorylation [#1]. Beyond catalysis, MEK1 activity is tuned by inhibitory phosphorylation at Thr286/Thr292 by p34cdc2, Cdk5, ERK, and Cdk1 [#2, #19], and by post-translational modifications including Cys341 S-sulfhydration that promotes nuclear ERK/PARP-1-dependent DNA repair [#5] and Lys175 acetylation controlled by SIRT2 that links MEK1-ERK to DRP1-driven mitochondrial fission [#6]. Functionally MEK1 is non-redundant with MEK2: it drives the G1/S transition through cyclin D1 induction and p27/p21 control [#16, #17], promotes epidermal proliferation in part through a kinase-independent mechanism [#15], confers cardioprotection against ischemia-reperfusion injury via ERK2 [#23], and limits the duration of macrophage proinflammatory ERK signaling to promote resolution of lung injury [#20, #21]. Recurrent activating MAP2K1 mutations cause constitutive ERK activation and MEK-inhibitor resistance in Langerhans cell histiocytosis and other cancers [#13, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established that MEK1 is not only activated by upstream kinases but is also negatively controlled, defining a cell-cycle-linked inhibitory mechanism.\",\n      \"evidence\": \"In vitro kinase assay with p34cdc2 plus in vivo phosphorylation mapping and mutagenesis of Thr286/Thr292\",\n      \"pmids\": [\"8114697\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how inhibitory phosphorylation is reversed\", \"Functional consequence for ERK output not quantified in this study\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Demonstrated that MEK1 activity is sufficient to drive proliferation and transformation, linking the kinase directly to cell-cycle machinery.\",\n      \"evidence\": \"Inducible constitutively active MEK1-ER fusion in NIH-3T3 cells with cell-cycle, cyclin D1/p27, and transformation assays\",\n      \"pmids\": [\"9582373\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether endogenous MEK1 sets the same thresholds was untested\", \"Does not distinguish MEK1 from MEK2 contributions\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed that MEK1 subcellular distribution is regulated, addressing where MEK1 acts during the cell cycle.\",\n      \"evidence\": \"Fluorescence microscopy of NES- and activation-site-mutant MEK1 constructs with inhibitor and synchronization in cultured cells\",\n      \"pmids\": [\"10037701\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Nuclear substrates of MEK1 not identified\", \"Single-lab localization study\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined an upstream regulatory input by showing MEKK1 autoubiquitylation gates its ability to phosphorylate MKK1.\",\n      \"evidence\": \"In vitro kinase and ubiquitylation assays with MEKK1 PHD-domain mutagenesis\",\n      \"pmids\": [\"12456688\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological contexts where MEKK1 controls MEK1 unclear\", \"Did not map MEK1 phosphosites targeted by MEKK1\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Resolved that MEK1 and MEK2 have non-redundant roles, with MEK1 specifically required to restrain G1/S progression and prevent senescence.\",\n      \"evidence\": \"Isoform-specific RNAi knockdown with cell-cycle, cyclin D1/p21, and colony-formation readouts; transgenic epidermal and cardiac models\",\n      \"pmids\": [\"15284233\", \"15342384\", \"15096454\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of MEK1 vs MEK2 substrate/output divergence not defined\", \"Kinase-independent epidermal function mechanism unresolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified WNK2 as an upstream negative regulator acting at the MEK1 level, expanding the network controlling pathway suppression.\",\n      \"evidence\": \"RNAi knockdown and kinase-dead WNK2 mutant with pMEK1(S298)/pERK readouts in HeLa and HT29 cells\",\n      \"pmids\": [\"17667937\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether WNK2 acts directly on MEK1 not shown\", \"Mechanism connecting WNK2 to Ser298 phosphorylation unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Discovered the MEK1-MEK2 heterodimer and established MEK1 as the master modulator of pathway duration through Thr292 feedback.\",\n      \"evidence\": \"Reciprocal Co-IP, phosphosite mutagenesis, and MEK1 knockout mouse with in vivo ERK/MEK phosphorylation assays\",\n      \"pmids\": [\"19219045\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural geometry of the heterodimer not resolved\", \"Quantitative contribution of heterodimer vs homodimer to ERK output unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Consolidated the activating and inhibitory phosphosite map and the KSR scaffold requirement into a coherent activation model.\",\n      \"evidence\": \"Synthesis of phosphosite mapping, kinase assay, and mutagenesis data (review)\",\n      \"pmids\": [\"22177953\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Review-level synthesis rather than new primary data\", \"Dynamic interplay among phosphosites not quantified\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealed a redox-sensing modification on MEK1 that couples H2S signaling to nuclear ERK-dependent DNA repair.\",\n      \"evidence\": \"S-sulfhydration assay, Cys341 mutagenesis, MEK1-PARP-1 Co-IP, nuclear ERK immunofluorescence, and DNA damage assays\",\n      \"pmids\": [\"24778456\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding without independent replication\", \"Stoichiometry and physiological H2S thresholds undefined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defined a tissue-specific MEK1 role in restraining macrophage M2 polarization and efferocytosis, separable from STAT6.\",\n      \"evidence\": \"Conditional Mek1 knockout, pharmacological MEKi, STAT6 KO epistasis, and in vivo efferocytosis and lung injury models\",\n      \"pmids\": [\"28003382\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"MEK1 substrates governing efferocytosis genes not identified\", \"STAT6-independent efferocytosis mechanism unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Classified oncogenic MEK1 mutations by mechanism and established dimerization as essential for both activation and catalysis.\",\n      \"evidence\": \"In vitro kinase and dimerization assays, mutagenesis, inhibitor-sensitivity assays, and xenograft models\",\n      \"pmids\": [\"30377225\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of homodimer cross-phosphorylation not directly visualized\", \"In vivo prevalence of each mutation class not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided the structural basis for MEK1 autoinhibition and activation within the 14-3-3-cradled BRAF complex.\",\n      \"evidence\": \"Cryo-EM of full-length BRAF-MEK1-14-3-3 complexes in autoinhibited and active states\",\n      \"pmids\": [\"31581174\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"MEK1 catalytic transition state not captured\", \"Role of MEK2 in analogous complexes not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Characterized a clinically acquired gatekeeper mutation that uncouples MEK1 from allosteric inhibition while retaining ATP-competitive vulnerability.\",\n      \"evidence\": \"Whole-genome sequencing of patient tumor with MEK1 kinase, drug-affinity, and in vivo sensitivity assays for V211D\",\n      \"pmids\": [\"31227518\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generality across other allosteric inhibitors beyond those tested\", \"Resistance evolution dynamics in patients not tracked\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Mapped how arrestin-2 scaffolds the cRAF-MEK1-ERK2 cascade and how MEK1 nucleotide state gates the interaction.\",\n      \"evidence\": \"HDX-MS, tryptophan-induced bimane fluorescence quenching, and NMR interface mapping\",\n      \"pmids\": [\"34507982\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular consequences of scaffolded geometry not quantified\", \"Whether MEK2 is similarly scaffolded unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extended MEK1 regulation to acetylation, linking SIRT2-MEK1-ERK to DRP1-driven mitochondrial dynamics.\",\n      \"evidence\": \"Acetylation mass spectrometry, Lys175 site identification, and ERK/DRP1 phosphorylation with mitochondrial imaging upon SIRT2 perturbation\",\n      \"pmids\": [\"34965411\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding\", \"Acetyltransferase opposing SIRT2 not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrated in vivo that MEK1 limits the duration of macrophage proinflammatory ERK signaling to enable resolution of lung injury.\",\n      \"evidence\": \"Conditional LysMCre Mek1 knockout in LPS-induced acute lung injury with macrophage MEK2/ERK phosphorylation readouts\",\n      \"pmids\": [\"31801908\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between MEK1 loss and failed resolution incompletely defined\", \"Relative roles of MEK2 derepression vs direct MEK1 loss unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Proposed SUMOylation as an additional negative regulatory modification of MEK1.\",\n      \"evidence\": \"SUMOylation assays and proliferation/invasion readouts in ovarian cancer cells and xenografts after monensin treatment\",\n      \"pmids\": [\"34650638\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"SUMO acceptor sites and responsible E3 ligase not identified\", \"Correlative rather than direct causal evidence\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Offered an atomistic rationale for how BRAF versus KSR1 differentially position the MEK1 activation loop for phosphorylation.\",\n      \"evidence\": \"Molecular dynamics simulations of B-Raf/MEK1 and KSR1/MEK1 heterodimers\",\n      \"pmids\": [\"35508574\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Computational only, no experimental validation in this study\", \"Predicted P-rich loop role not tested by mutagenesis\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many regulatory inputs on MEK1 — activating and inhibitory phosphorylation, S-sulfhydration, acetylation, SUMOylation, dimerization state, and scaffold occupancy — are integrated dynamically to set ERK signal amplitude and duration in a given cell type remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified quantitative model integrating MEK1 PTMs and dimerization\", \"Cell-type-specific weighting of regulatory inputs undefined\", \"Structural state of catalytically active MEK1 toward ERK not captured\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3, 8, 13, 18]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [3, 8, 13]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 3, 8]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [2, 16, 17]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [13, 14, 8]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [20, 21]}\n    ],\n    \"complexes\": [\n      \"BRAF-MEK1-14-3-3 complex\",\n      \"MEK1-MEK2 heterodimer\",\n      \"cRAF-MEK1-ERK2 arrestin-2 scaffold complex\"\n    ],\n    \"partners\": [\n      \"BRAF\",\n      \"KSR1\",\n      \"MAP2K2\",\n      \"MAPK1\",\n      \"RAF1\",\n      \"ARRB1\",\n      \"PARP1\",\n      \"SIRT2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}