{"gene":"MAPKAPK5","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":1998,"finding":"PRAK (MAPKAPK5) is a serine/threonine kinase activated by p38α and p38β both in vitro and in vivo; Thr182 was identified as the regulatory phosphorylation site. Activated PRAK phosphorylates small heat shock protein 27 (HSP27) at physiologically relevant sites.","method":"In vitro kinase assay, in-gel kinase assay, mutagenesis of Thr182, co-immunoprecipitation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis of regulatory site, replicated by multiple methods in founding paper","pmids":["9628874"],"is_preprint":false},{"year":1998,"finding":"MAPKAPK5 can be phosphorylated and activated by ERK and p38 kinase in vitro (but not by JNK); phosphorylation by ERK and p38 increased its activity 9- and 15-fold respectively. Recombinant MAPKAPK5 phosphorylates a peptide derived from the regulatory light chain of myosin II.","method":"In vitro kinase assay with recombinant proteins","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution, single lab, single study","pmids":["9480836"],"is_preprint":false},{"year":2003,"finding":"Unlike MK2, endogenous MK5 does not interact with or chaperone p38 MAPK, is not activated by extracellular stresses such as arsenite or sorbitol, and cannot phosphorylate Hsp27 in vitro and in vivo in fibroblasts derived from knockout mice.","method":"MK5 knockout mouse fibroblasts, in vitro kinase assay, co-immunoprecipitation","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — knockout mouse model with multiple orthogonal assays; negative findings rigorously established","pmids":["14560018"],"is_preprint":false},{"year":2003,"finding":"PRAK subcellular localization is controlled by p38α and p38β through docking interactions: ectopically expressed PRAK resides in the nucleus but is redistributed to cytoplasm by co-expression of p38α/β. p38-mediated phosphorylation of PRAK promotes its nuclear export, while nuclear import is p38-independent. PRAK contains functional NES and NLS motifs required for nucleocytoplasmic shuttling.","method":"Immunostaining, nuclear export/import assays, docking groove and docking-site mutants, leptomycin B treatment","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (mutagenesis, imaging, pharmacological inhibition), single lab","pmids":["12808055"],"is_preprint":false},{"year":2004,"finding":"ERK3 specifically interacts with MK5, causing nuclear exclusion of both proteins and ERK3-dependent phosphorylation and activation of MK5 in vitro and in vivo. Endogenous MK5 activity is reduced by siRNA knockdown of ERK3 and in ERK3-/- fibroblasts. MK5 acts as a chaperone for ERK3 (MK5 depletion dramatically reduces ERK3 protein levels).","method":"Co-immunoprecipitation, siRNA knockdown, ERK3 knockout fibroblasts, in vitro kinase assay, immunofluorescence","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, knockout cells, siRNA, in vitro assay; independently replicated in companion paper (PMID:15538386)","pmids":["15577943"],"is_preprint":false},{"year":2004,"finding":"ERK3 scaffolds MK5 activation independent of ERK3 enzymatic activity but dependent on MK5 catalytic activity and the C-terminal extension of ERK3. ERK3-MK5 interaction causes nuclear-to-cytoplasmic translocation of MK5. MK5 deletion causes strong reduction of ERK3 protein levels and embryonic lethality at ~E11 in mice.","method":"Co-immunoprecipitation, kinase-dead mutants, MK5 knockout mouse, immunofluorescence, embryo analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mouse phenotype, mutant rescue experiments, reciprocal interaction assays; replicated across two concurrent papers","pmids":["15538386"],"is_preprint":false},{"year":2006,"finding":"ERK4 (MAPK4), a stable protein, binds endogenous MK5 and translocates MK5 to the cytoplasm. Unlike ERK3, ERK4 requires its own catalytic activity to activate MK5 (direct phosphorylation). ERK4 can dimerize/oligomerize with ERK3, enabling ERK4 to relay activation to MK5 in the context of kinase-dead ERK3.","method":"Co-immunoprecipitation, kinase-dead mutants, transfection in HEK293 cells, immunofluorescence","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with mutant analysis, single lab, two orthogonal methods","pmids":["16973613"],"is_preprint":false},{"year":2007,"finding":"PRAK activates p53 by direct phosphorylation, mediating oncogenic ras-induced senescence downstream of p38 MAPK. PRAK deficiency in mice enhances DMBA-induced skin carcinogenesis coinciding with impaired senescence induction.","method":"In vitro kinase assay, PRAK knockout mice, primary cell transformation assay, DMBA skin carcinogenesis model","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro direct phosphorylation, knockout mouse carcinogenesis model, multiple orthogonal methods","pmids":["17254968"],"is_preprint":false},{"year":2007,"finding":"PKA catalytic subunit Cα interacts with MK5 (but not MK2) in vivo, increases MK5 kinase activity and phosphorylation, and induces transient nuclear export of MK5, which requires kinase activity of both Cα and MK5 and Cα nuclear entry. MK5 is required for PKA-induced F-actin rearrangement in PC12 cells.","method":"Co-immunoprecipitation, kinase assays, siRNA depletion, constitutively active MK5 expression, fluorescence microscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, siRNA rescue, multiple functional readouts, single lab","pmids":["17947239"],"is_preprint":false},{"year":2007,"finding":"14-3-3ε interacts with MK5 in vivo and in vitro, and this interaction inhibits MK5-mediated phosphorylation of HSP27, thereby disrupting F-actin polymerization and inhibiting MK5-induced cell migration.","method":"Co-immunoprecipitation, in vitro binding assay, transfection, cell migration assay","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP plus functional readout, single lab","pmids":["17728103"],"is_preprint":false},{"year":2008,"finding":"Activation loop phosphorylation of ERK3 and ERK4 (at their SEG motif) is required for formation of stable active complexes with MK5 and for efficient cytoplasmic redistribution of ERK3/ERK4-MK5 complexes. This phosphorylation is constitutive in resting cells and can be modulated by MK5 interaction.","method":"Phospho-specific antibodies, mutagenesis of SEG motif, co-immunoprecipitation, subcellular fractionation","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis combined with Co-IP and localization assays, single lab","pmids":["18720373"],"is_preprint":false},{"year":2008,"finding":"ERK4 Ser186 (in its SEG motif) is phosphorylated in vivo by an upstream kinase (not autophosphorylation); Ser186 phosphorylation is required for ERK4 to interact with, activate, and cytoplasmatically anchor MK5. MK5 binding facilitates Ser186 phosphorylation and stabilizes the ERK4-MK5 complex.","method":"Mutagenesis of Ser186, phospho-specific antibodies, co-immunoprecipitation, kinase assays","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — site-directed mutagenesis plus functional kinase assay, single lab","pmids":["18248330"],"is_preprint":false},{"year":2008,"finding":"Distinct amino acid residues in p38α (Asp145, Leu156) versus p38β (Gly145, Val156) determine the differential subcellular localization of p38α-PRAK (nuclear) versus p38β-PRAK (cytosolic) complexes. Nuclear localization of PRAK is required for its function in inhibiting NIH3T3 cell proliferation.","method":"Chimeric and point mutants of p38α/β, immunofluorescence, nuclear import/export assays, cell proliferation assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis with localization and functional readout, single lab","pmids":["18268017"],"is_preprint":false},{"year":2009,"finding":"ERK3 and ERK4 contain a novel MK5-interaction motif (FRIEDE) in their L16 C-terminal extension, distinct from the classical CD domain. A single I→K substitution in FRIEDE abolishes binding, activation, and translocation of MK5 by both ERK3 and ERK4. Activation loop phosphorylation of ERK3/4 gates accessibility of the FRIEDE motif.","method":"Peptide overlay assays, mutagenesis of FRIEDE motif, co-immunoprecipitation, kinase activation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — mutagenesis defining interaction motif with multiple functional readouts (binding, activation, localization), single lab","pmids":["19473979"],"is_preprint":false},{"year":2009,"finding":"MK5 interacts with HSP27 in vivo and phosphorylates HSP27 at Ser78 and Ser82 in cells. Expression of constitutively active MK5 induces F-actin rearrangement in PC12 cells, and co-expression of non-phosphorylatable Hsp27-3A abrogates this effect.","method":"Co-immunoprecipitation, phospho-specific antibodies, constitutively active MK5 expression, siRNA depletion of Hsp27, fluorescence microscopy","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with functional mutant rescue, single lab","pmids":["19166925"],"is_preprint":false},{"year":2010,"finding":"PKA phosphorylates MK5 at Ser115 in vitro; PKA-induced nuclear export of MK5 requires Ser115 phosphorylation (S115A blocks PKA-induced export; S115D phosphomimetic causes cytoplasmic localization in resting cells). Mutations in Ser115 affect MK5 biological properties.","method":"In vitro kinase assay, mutagenesis of Ser115, nuclear export assay, phosphomimetic mutant analysis","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro phosphorylation with site-directed mutagenesis and functional localization readout, single lab","pmids":["20734105"],"is_preprint":false},{"year":2011,"finding":"MK5 regulates translation of c-Myc by promoting expression of miR-34b and miR-34c through phosphorylation of FoxO3a, which promotes nuclear localization of FoxO3a enabling it to induce miR-34b/c expression. This establishes a MK5-FoxO3a-miR-34b/c negative feedback loop that suppresses Myc and is disrupted in colorectal cancer.","method":"siRNA kinome screen, reporter assays, FoxO3a phosphorylation assay, nuclear localization of FoxO3a by immunofluorescence, miRNA expression analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — kinome siRNA screen followed by mechanistic dissection with multiple orthogonal methods, single lab with strong evidence","pmids":["21329882"],"is_preprint":false},{"year":2011,"finding":"MK5 activates FoxO3a by phosphorylation in developing B cells; this MK5-mediated phosphorylation of Foxo1 at Ser215 is required for transcriptional activation of Rag genes. MK5 is necessary and sufficient to activate Rag transcription in pro-B cells.","method":"Foxo1 mutant panel screen, in vitro and in vivo phosphorylation, B cell transformation and primary pro-B cell assays","journal":"The Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site identification by mutant panel, functional rescue in primary cells, single lab","pmids":["23878308"],"is_preprint":false},{"year":2011,"finding":"The p38β-PRAK cascade mediates energy-starvation-induced suppression of mTORC1. PRAK directly phosphorylates Rheb at Ser130, impairing Rheb nucleotide-binding ability and inhibiting Rheb-mediated mTORC1 activation. This pathway operates independently of AMPK-TSC2 and AMPK-Raptor pathways.","method":"In vitro kinase assay, Rheb phosphorylation mapping, siRNA depletion, mTORC1 activity assays, cell-size measurement","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct in vitro phosphorylation with site mapping, epistasis experiments, and multiple functional readouts","pmids":["21336308"],"is_preprint":false},{"year":2012,"finding":"In IGF2BP1-expressing tumor cells, inhibition of MAPK4 mRNA translation by IGF2BP1 antagonizes MK5 activation and prevents MK5-mediated HSP27 phosphorylation, which would otherwise sequester actin monomers, reducing availability of G-actin for F-actin polymerization and cell migration.","method":"Translational inhibition assay, MK5 activity measurements, HSP27 phosphorylation, F-actin/G-actin assays, cell migration assay","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical assays linking MAPK4-MK5-HSP27-actin axis, single lab","pmids":["22279049"],"is_preprint":false},{"year":2013,"finding":"Tip60 acetylates PRAK at K364 in a manner that depends on prior phosphorylation of both Tip60 (Thr158 by p38) and PRAK by p38, inducing PRAK kinase activity. This defines a cascade: ras→p38→Tip60 acetylation→PRAK activation→oncogene-induced senescence.","method":"In vitro acetyltransferase assay, mutagenesis of Tip60-Thr158 and PRAK-K364, co-immunoprecipitation, senescence assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — biochemical reconstitution of PTM cascade with mutagenesis and functional senescence readout","pmids":["23685072"],"is_preprint":false},{"year":2013,"finding":"MK5 physically interacts with Hsp40/DnaJB1 in cells via C-terminal regions of both proteins and phosphorylates Hsp40/DnaJB1 at Ser149 and/or Ser151 and Ser171 in vivo. MK5 modestly stimulates Hsp40/Hsp70 ATPase activity and enhances Hsp40/DnaJB1-mediated repression of HSF1-driven transcription.","method":"Co-immunoprecipitation, in vitro kinase assay, phospho-specific antibodies, ATPase activity assay, luciferase reporter assay","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus in vitro phosphorylation and functional assays, single lab","pmids":["24309468"],"is_preprint":false},{"year":2014,"finding":"PRAK interacts with DJ-1 (via yeast two-hybrid confirmed by Co-IP) and phosphorylates DJ-1 in vitro and in vivo upon H2O2 stimulation. In PRAK-/- cells, DJ-1 translocates from nucleus to cytoplasm after H2O2, losing its ability to sequester the pro-apoptotic protein Daxx in the nucleus, leading to cell death.","method":"Yeast two-hybrid, Co-immunoprecipitation, in vitro kinase assay, immunofluorescence in PRAK+/+ vs PRAK-/- cells, Daxx localization assay","journal":"Oxidative medicine and cellular longevity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid confirmed by Co-IP and phosphorylation, functional localization in knockout cells, single lab","pmids":["25383140"],"is_preprint":false},{"year":2014,"finding":"PRAK is phosphorylated by Src kinase, directing PRAK to focal adhesions. Overexpressed PRAK inhibits cell motility by phosphorylating FAK at Y861, thereby impairing FAK activation. PRAK and Src/FAK interact physically in focal adhesions.","method":"In situ kinase overlay assay, co-immunoprecipitation, phospho-specific antibodies for FAK Y861, motility assay, immunofluorescence","journal":"Journal of cancer biology & research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, journal not peer-reviewed at high tier, limited validation methods","pmids":["26042227"],"is_preprint":false},{"year":2016,"finding":"PRAK interacts with RAGE (receptor for advanced glycation end-products) and Aβ treatment increases PRAK phosphorylation and PRAK-RAGE interaction. PRAK knockdown rescues mTORC1 inactivation induced by Aβ and decreases Aβ-induced autophagosome formation, placing PRAK in the RAGE-mTORC1-autophagy pathway in Alzheimer's disease models.","method":"Co-immunoprecipitation, siRNA knockdown, mTORC1 activity assay, autophagosome quantification","journal":"Molecular neurodegeneration","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, Co-IP with functional assay, limited mechanistic validation","pmids":["26758977"],"is_preprint":false},{"year":2019,"finding":"MK5 physically interacts with YAP and counteracts CK1δ/ε-mediated YAP ubiquitination and degradation in a LATS1/2-independent manner. MK5 kinase activity is essential for protecting YAP from ubiquitin-mediated degradation and cytoplasmic retention.","method":"RNAi screen, co-immunoprecipitation, ubiquitination assay, kinase-dead MK5 mutant, xenograft model","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi screen followed by Co-IP, ubiquitination assay, and mutant analysis; single lab","pmids":["31578200"],"is_preprint":false},{"year":2021,"finding":"Loss-of-function variants in MAPKAPK5 cause a developmental disorder with neurological, cardiac, and digital anomalies. Patient-derived fibroblasts lack MAPKAPK5 protein isoforms, have reduced ERK3 levels, and show impaired F-actin recovery after latrunculin B treatment, supporting a role of MAPKAPK5 in F-actin polymerization.","method":"Exome sequencing, patient-derived fibroblast functional assays (F-actin recovery after latrunculin B treatment), Western blot","journal":"Genetics in medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient-derived cells with direct functional assay, two independent families; mechanistic link to F-actin confirmed","pmids":["33442026"],"is_preprint":false},{"year":2021,"finding":"PRAK deficiency abrogates lung metastases in PyMT mice and after intravenous injection of tumor cells, with no effect on primary tumor growth. Loss of PRAK leads to pronounced inhibition of HIF-1α protein synthesis, possibly due to reduced mTORC1 activities.","method":"Prak knockout mouse models, PyMT mammary tumor model, intravenous tumor injection, Western blot for HIF-1α and mTORC1 components","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockout mouse with defined metastasis phenotype and molecular mechanism, single lab","pmids":["33741957"],"is_preprint":false},{"year":2022,"finding":"TLK1 phosphorylates MK5 at three residues (S160, S354, S386), resulting in MK5 activation. MK5-S354A or kinase-dead MK5 in MK5-/- MEF cells fails to restore motility compared to wild-type MK5. The TLK1-MK5 axis promotes prostate cancer cell motility and invasion.","method":"In vitro kinase assay, phospho-specific antibody for pMK5-S354, mutagenesis, MK5 knockout MEF rescue, motility assay","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-directed mutagenesis with functional rescue in knockout cells plus in vitro phosphorylation, single lab","pmids":["35064619"],"is_preprint":false},{"year":2022,"finding":"ERK3-MK5 signaling promotes FoxO3 degradation by MK5-mediated direct phosphorylation of FoxO3, reducing FoxO3 association with MyoD and inhibiting myogenic differentiation. Loss of ERK3 or MK5 causes precocious myoblast differentiation; depletion of FoxO3 rescues this premature differentiation.","method":"In vitro kinase assay, genetic inactivation of ERK3 (Mapk6KD/KD mice) and MK5, C2C12 and primary myoblast differentiation assays, FoxO3 depletion rescue experiments","journal":"Journal of cellular physiology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro phosphorylation, multiple genetic models (kinase-dead ERK3 mice, MK5 KO), epistasis with FoxO3, replicated in multiple cell types","pmids":["35141958"],"is_preprint":false},{"year":2023,"finding":"PRAK phosphorylates NRF2 at Ser558, enhancing NRF2 protein stability independent of ubiquitination. Loss of PRAK increases cellular ROS, disrupts glycolysis and PKM2-dependent STAT3 phosphorylation, and impairs Th17 cell differentiation. Prak KO mice show resistance to EAE but impaired antitumor immunity.","method":"In vitro kinase assay identifying NRF2 as MK5/PRAK substrate, Prak knockout mice, Th17 differentiation assays, ROS measurement, glycolysis assays","journal":"PNAS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct substrate identification with site mapping, knockout mouse phenotype, multiple pathway readouts, single lab","pmids":["37126714"],"is_preprint":false},{"year":2012,"finding":"Septin 8 is an interaction partner and in vitro substrate of MK5; the interaction is confirmed by GST pulldown, Co-IP, and FRET. MK5 phosphorylates Ser242 and Ser271 on Septin 8 in vitro. MK5 and Septin 8 co-localize in the perinuclear area, cell protrusions, and with synaptophysin-positive vesicles.","method":"Yeast two-hybrid, GST pulldown, Co-immunoprecipitation, FRET, in vitro kinase assay, confocal microscopy","journal":"World journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal binding assays plus in vitro phosphorylation and colocalization, single lab","pmids":["22649572"],"is_preprint":false},{"year":2026,"finding":"FXR1 drives retention of exon 6 in MK5 pre-mRNA, generating a long kinase-competent MK5-L isoform in HCC. MK5-L phosphorylates GSK3β, activating Wnt/β-catenin signaling and promoting HCC progression and metastasis.","method":"Alternative splicing analysis, in vitro kinase assay, GSK3β phosphorylation, Wnt/β-catenin reporter, FXR1 knockdown/overexpression, xenograft model, antisense oligonucleotide therapeutic intervention","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct substrate phosphorylation with splicing mechanism and functional in vivo validation, single lab","pmids":["41954085"],"is_preprint":false},{"year":2025,"finding":"Microglial MK5 regulates the neuroinflammatory response to ischemic stroke by controlling phosphorylation of HSP27 and NF-κB. Microglia-specific MK5 knockout exacerbates neurological deficits, increases infarct volume, upregulates pro-inflammatory cytokines, and reduces HSP27 phosphorylation while increasing NF-κB phosphorylation.","method":"Microglia-specific conditional MK5 knockout, MCAO mouse model, OGD/R BV2 cell model, Western blot for pHSP27 and pNF-κB, cytokine qPCR, immunofluorescence","journal":"CNS neuroscience & therapeutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional knockout with defined molecular mechanism (HSP27/NF-κB phosphorylation) and functional neurological readout, single lab","pmids":["40237440"],"is_preprint":false}],"current_model":"MAPKAPK5/PRAK/MK5 is a serine/threonine kinase activated downstream of both classical MAPKs (p38α/β, which phosphorylate its regulatory Thr182) and atypical MAPKs (ERK3 and ERK4, which bind MK5 via a FRIEDE motif in their C-terminal extension and translocate it to the cytoplasm), as well as PKA (which phosphorylates MK5 at Ser115 to drive nuclear export); once activated, MK5 phosphorylates a spectrum of substrates including HSP27 (regulating F-actin dynamics), p53 (mediating ras-induced senescence), Rheb-Ser130 (suppressing mTORC1 during energy starvation), FoxO3a (promoting miR-34b/c expression to suppress Myc and activating Rag transcription in B cells), NRF2-Ser558 (stabilizing NRF2 to maintain redox homeostasis in Th17 cells), FoxO3 (promoting its degradation to inhibit myogenic differentiation), and GSK3β (via a specific long MK5 splice isoform); MK5 also interacts with Hsp40/DnaJB1, Septin 8, YAP, DJ-1, and RAGE, and its subcellular localization (nuclear vs. cytoplasmic) is dynamically regulated by p38α/β docking interactions and phosphorylation, with distinct p38α versus p38β complexes targeting different compartments."},"narrative":{"mechanistic_narrative":"MAPKAPK5 (PRAK/MK5) is a serine/threonine kinase that integrates signals from classical and atypical MAP kinase pathways to control cytoskeletal dynamics, cellular senescence, growth, and stress responses [PMID:9628874, PMID:17254968]. It was originally defined as a p38α/β-activated kinase whose regulatory Thr182 is phosphorylated to drive activity toward HSP27, coupling MK5 to F-actin remodeling [PMID:9628874, PMID:19166925]. Distinct from MK2, endogenous MK5 does not chaperone p38 or respond to canonical extracellular stresses [PMID:14560018]; instead its activation and cytoplasmic anchoring are dominated by the atypical MAPKs ERK3 and ERK4, which bind MK5 through a FRIEDE motif in their C-terminal L16 extension, mutually stabilizing the partners and translocating MK5 out of the nucleus [PMID:15577943, PMID:15538386, PMID:19473979]. MK5 subcellular distribution is further tuned by p38α versus p38β docking, which respectively retain it in the nucleus or cytoplasm, and by PKA, which phosphorylates Ser115 to drive nuclear export [PMID:12808055, PMID:18268017, PMID:20734105]. Functionally, MK5 enforces oncogene-induced senescence by directly phosphorylating p53 downstream of a ras→p38→Tip60 acetylation cascade, with knockout mice showing enhanced carcinogenesis [PMID:17254968, PMID:23685072]. It additionally phosphorylates Rheb-Ser130 to suppress mTORC1 during energy starvation, FoxO transcription factors to control Myc-suppressing miR-34b/c and Rag transcription, NRF2-Ser558 to maintain redox homeostasis, and GSK3β via a long splice isoform, linking MK5 to metabolic, immune, and Wnt signaling outputs [PMID:21336308, PMID:21329882, PMID:23878308, PMID:37126714, PMID:41954085]. Loss-of-function variants in MAPKAPK5 cause a developmental disorder with neurological, cardiac, and digital anomalies, with patient fibroblasts showing reduced ERK3 levels and impaired F-actin recovery [PMID:33442026].","teleology":[{"year":1998,"claim":"Established MK5/PRAK as a p38-activated kinase and identified its regulatory phosphorylation site and a first substrate, defining where it sits in stress signaling.","evidence":"In vitro and in-gel kinase assays with Thr182 mutagenesis and Co-IP, plus parallel recombinant kinase work showing ERK/p38 activation","pmids":["9628874","9480836"],"confidence":"High","gaps":["Physiological upstream activator in vivo not resolved among p38/ERK","Substrate spectrum beyond HSP27/myosin light chain peptide unknown"]},{"year":2003,"claim":"Distinguished MK5 from MK2 and showed its localization is governed by p38 docking, redefining MK5 as a distinct enzyme rather than a p38 chaperone.","evidence":"MK5 knockout fibroblasts with kinase and Co-IP assays; imaging plus NES/NLS mutants and leptomycin B","pmids":["14560018","12808055"],"confidence":"High","gaps":["Conflicts with founding HSP27 substrate claim left unreconciled","True physiological activator still unidentified at this stage"]},{"year":2004,"claim":"Identified ERK3 (and later ERK4) as the atypical MAPK partners that bind, activate, and cytoplasmically anchor MK5, resolving the missing upstream activator and revealing reciprocal protein stabilization.","evidence":"Reciprocal Co-IP, siRNA, ERK3/MK5 knockout fibroblasts and embryonic-lethal mice, kinase-dead mutants, immunofluorescence","pmids":["15577943","15538386","16973613"],"confidence":"High","gaps":["Why ERK3 acts catalysis-independently while ERK4 requires its own activity","Physiological signals that engage the ERK3/4-MK5 module unknown"]},{"year":2007,"claim":"Linked MK5 to tumor suppression by showing it phosphorylates p53 to drive ras-induced senescence, and to PKA signaling controlling actin remodeling, expanding MK5 into cell-fate and cytoskeletal control.","evidence":"In vitro kinase assays, PRAK knockout mice with DMBA carcinogenesis, transformation assays; PKA Cα Co-IP, siRNA, F-actin readouts","pmids":["17254968","17947239","17728103"],"confidence":"High","gaps":["Whether p38-MK5-p53 axis operates beyond ras-driven contexts","Relative contribution of nuclear vs cytoplasmic MK5 pools to each output"]},{"year":2009,"claim":"Defined the FRIEDE motif as the structural basis of ERK3/4-MK5 binding and confirmed HSP27-Ser78/82 as a cellular substrate, mechanizing both complex assembly and cytoskeletal output.","evidence":"Peptide overlay and FRIEDE mutagenesis with binding/activation/localization readouts; phospho-specific antibodies and Hsp27-3A rescue","pmids":["19473979","19166925","18720373","18248330","18268017"],"confidence":"High","gaps":["Identity of the kinase phosphorylating ERK4 SEG motif","How activation-loop phosphorylation gates FRIEDE accessibility mechanistically"]},{"year":2011,"claim":"Connected MK5 to growth and transcriptional control by identifying Rheb-Ser130 (mTORC1 suppression) and FoxO3a/Foxo1 (miR-34b/c-Myc loop, Rag activation) as direct substrates.","evidence":"In vitro kinase assays with site mapping, kinome/mutant screens, reporter assays, epistasis, and primary B-cell rescue","pmids":["21336308","21329882","23878308"],"confidence":"High","gaps":["How a single kinase selects between cytoskeletal, senescence, and transcriptional substrates","In vivo significance of MK5-Rheb axis across tissues"]},{"year":2013,"claim":"Resolved the activation logic of MK5 in senescence as a PTM cascade (p38-dependent Tip60 acetylation of PRAK-K364) and added Hsp40/DnaJB1 as a substrate, refining the activation and chaperone interface.","evidence":"In vitro acetyltransferase and kinase assays with Tip60-T158/PRAK-K364 mutagenesis, Co-IP, senescence and ATPase/reporter assays","pmids":["23685072","24309468"],"confidence":"High","gaps":["Generality of acetylation-dependent activation beyond ras senescence","Functional consequence of Hsp40 phosphorylation in vivo"]},{"year":2014,"claim":"Extended MK5 into oxidative-stress and motility control through interactions with DJ-1, Septin 8, and Src/FAK, implicating it in apoptosis regulation and focal-adhesion dynamics.","evidence":"Yeast two-hybrid, Co-IP, FRET, in vitro phosphorylation, knockout-cell localization assays; Src/FAK overlay and motility assays","pmids":["25383140","22649572","26042227"],"confidence":"Medium","gaps":["Src/FAK axis rests on a single low-tier study without independent confirmation","Physiological stimuli engaging DJ-1 and Septin 8 phosphorylation unclear"]},{"year":2019,"claim":"Implicated MK5 in Hippo and metastasis biology by showing it protects YAP from CK1-mediated degradation and is required for HIF-1α synthesis and lung metastasis.","evidence":"RNAi screen, Co-IP, ubiquitination assays, kinase-dead mutant, xenografts; PRAK knockout PyMT and IV-injection metastasis models","pmids":["31578200","33741957"],"confidence":"Medium","gaps":["Direct YAP phosphorylation site not defined","Mechanistic link between MK5, mTORC1, and HIF-1α translation incomplete"]},{"year":2021,"claim":"Established MAPKAPK5 as a disease gene, with loss-of-function variants causing a multisystem developmental disorder and confirming the F-actin role in patient cells.","evidence":"Exome sequencing in two families, patient fibroblast F-actin recovery assays, Western blot for MK5 isoforms and ERK3","pmids":["33442026"],"confidence":"Medium","gaps":["Which substrate pathways drive the cardiac and digital phenotypes","Genotype-phenotype correlation across variant types"]},{"year":2026,"claim":"Broadened the MK5 substrate repertoire across immunity, neuroinflammation, alternative upstream kinases, and cancer-specific splice isoforms, showing context-dependent rewiring of the kinase.","evidence":"In vitro kinase assays and site mapping (NRF2-Ser558, GSK3β), Prak/MK5 knockout and conditional knockout mice (Th17/EAE, MCAO stroke), TLK1 phosphorylation rescue, FXR1-driven exon-6 splicing with ASO intervention","pmids":["37126714","40237440","35064619","35141958","41954085"],"confidence":"Medium","gaps":["How distinct upstream kinases (TLK1, Src, PKA, p38, ERK3/4) are selected in each context","Whether splice-isoform-specific substrate selectivity generalizes beyond HCC"]},{"year":null,"claim":"How MK5 achieves substrate selectivity among its many targets and which upstream activator dominates in a given physiological setting remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model linking activator identity to substrate output","Structural basis of isoform- and compartment-specific substrate choice unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,7,14,16,18,21,22,28,29,30,31,32]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,7,18,30]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,5,25]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,12,16]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3,4,5,6,12]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[14,19,23]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,4,8,18,25]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[7,20,22]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[18,22,30]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[7,20,12]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[17,30]}],"complexes":["ERK3-MK5 complex","ERK4-MK5 complex","p38-MK5 complex"],"partners":["MAPK6","MAPK4","MAPK14","PRKACA","YWHAE","DNAJB1","PARK7","SEPT8"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8IW41","full_name":"MAP kinase-activated protein kinase 5","aliases":["p38-regulated/activated protein kinase","PRAK"],"length_aa":473,"mass_kda":54.2,"function":"Tumor suppressor serine/threonine-protein kinase involved in mTORC1 signaling and post-transcriptional regulation. Phosphorylates FOXO3, ERK3/MAPK6, ERK4/MAPK4, HSP27/HSPB1, p53/TP53 and RHEB. Acts as a tumor suppressor by mediating Ras-induced senescence and phosphorylating p53/TP53. Involved in post-transcriptional regulation of MYC by mediating phosphorylation of FOXO3: phosphorylation of FOXO3 leads to promote nuclear localization of FOXO3, enabling expression of miR-34b and miR-34c, 2 post-transcriptional regulators of MYC that bind to the 3'UTR of MYC transcript and prevent MYC translation. Acts as a negative regulator of mTORC1 signaling by mediating phosphorylation and inhibition of RHEB. Part of the atypical MAPK signaling via its interaction with ERK3/MAPK6 or ERK4/MAPK4: the precise role of the complex formed with ERK3/MAPK6 or ERK4/MAPK4 is still unclear, but the complex follows a complex set of phosphorylation events: upon interaction with atypical MAPK (ERK3/MAPK6 or ERK4/MAPK4), ERK3/MAPK6 (or ERK4/MAPK4) is phosphorylated and then mediates phosphorylation and activation of MAPKAPK5, which in turn phosphorylates ERK3/MAPK6 (or ERK4/MAPK4). Mediates phosphorylation of HSP27/HSPB1 in response to PKA/PRKACA stimulation, inducing F-actin rearrangement","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q8IW41/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MAPKAPK5","classification":"Not Classified","n_dependent_lines":58,"n_total_lines":1208,"dependency_fraction":0.048013245033112585},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MAPKAPK5","total_profiled":1310},"omim":[{"mim_id":"619869","title":"NEUROCARDIOFACIODIGITAL SYNDROME; NCFD","url":"https://www.omim.org/entry/619869"},{"mim_id":"606723","title":"MITOGEN-ACTIVATED PROTEIN KINASE-ACTIVATED PROTEIN KINASE 5; MAPKAPK5","url":"https://www.omim.org/entry/606723"},{"mim_id":"602195","title":"HEAT-SHOCK 27-KD PROTEIN 1; HSPB1","url":"https://www.omim.org/entry/602195"},{"mim_id":"600289","title":"MITOGEN-ACTIVATED PROTEIN KINASE 14; MAPK14","url":"https://www.omim.org/entry/600289"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MAPKAPK5"},"hgnc":{"alias_symbol":["PRAK","MK5"],"prev_symbol":[]},"alphafold":{"accession":"Q8IW41","domains":[{"cath_id":"3.30.200.20","chopping":"1-104","consensus_level":"medium","plddt":87.7763,"start":1,"end":104},{"cath_id":"1.10.510.10","chopping":"107-176_217-339","consensus_level":"high","plddt":84.8007,"start":107,"end":339},{"cath_id":"-","chopping":"382-470","consensus_level":"high","plddt":81.001,"start":382,"end":470}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IW41","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IW41-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IW41-F1-predicted_aligned_error_v6.png","plddt_mean":78.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MAPKAPK5","jax_strain_url":"https://www.jax.org/strain/search?query=MAPKAPK5"},"sequence":{"accession":"Q8IW41","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8IW41.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8IW41/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IW41"}},"corpus_meta":[{"pmid":"9628874","id":"PMC_9628874","title":"PRAK, 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Activated PRAK phosphorylates small heat shock protein 27 (HSP27) at physiologically relevant sites.\",\n      \"method\": \"In vitro kinase assay, in-gel kinase assay, mutagenesis of Thr182, co-immunoprecipitation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis of regulatory site, replicated by multiple methods in founding paper\",\n      \"pmids\": [\"9628874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"MAPKAPK5 can be phosphorylated and activated by ERK and p38 kinase in vitro (but not by JNK); phosphorylation by ERK and p38 increased its activity 9- and 15-fold respectively. Recombinant MAPKAPK5 phosphorylates a peptide derived from the regulatory light chain of myosin II.\",\n      \"method\": \"In vitro kinase assay with recombinant proteins\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution, single lab, single study\",\n      \"pmids\": [\"9480836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Unlike MK2, endogenous MK5 does not interact with or chaperone p38 MAPK, is not activated by extracellular stresses such as arsenite or sorbitol, and cannot phosphorylate Hsp27 in vitro and in vivo in fibroblasts derived from knockout mice.\",\n      \"method\": \"MK5 knockout mouse fibroblasts, in vitro kinase assay, co-immunoprecipitation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — knockout mouse model with multiple orthogonal assays; negative findings rigorously established\",\n      \"pmids\": [\"14560018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PRAK subcellular localization is controlled by p38α and p38β through docking interactions: ectopically expressed PRAK resides in the nucleus but is redistributed to cytoplasm by co-expression of p38α/β. p38-mediated phosphorylation of PRAK promotes its nuclear export, while nuclear import is p38-independent. PRAK contains functional NES and NLS motifs required for nucleocytoplasmic shuttling.\",\n      \"method\": \"Immunostaining, nuclear export/import assays, docking groove and docking-site mutants, leptomycin B treatment\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (mutagenesis, imaging, pharmacological inhibition), single lab\",\n      \"pmids\": [\"12808055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ERK3 specifically interacts with MK5, causing nuclear exclusion of both proteins and ERK3-dependent phosphorylation and activation of MK5 in vitro and in vivo. Endogenous MK5 activity is reduced by siRNA knockdown of ERK3 and in ERK3-/- fibroblasts. MK5 acts as a chaperone for ERK3 (MK5 depletion dramatically reduces ERK3 protein levels).\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, ERK3 knockout fibroblasts, in vitro kinase assay, immunofluorescence\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, knockout cells, siRNA, in vitro assay; independently replicated in companion paper (PMID:15538386)\",\n      \"pmids\": [\"15577943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ERK3 scaffolds MK5 activation independent of ERK3 enzymatic activity but dependent on MK5 catalytic activity and the C-terminal extension of ERK3. ERK3-MK5 interaction causes nuclear-to-cytoplasmic translocation of MK5. MK5 deletion causes strong reduction of ERK3 protein levels and embryonic lethality at ~E11 in mice.\",\n      \"method\": \"Co-immunoprecipitation, kinase-dead mutants, MK5 knockout mouse, immunofluorescence, embryo analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mouse phenotype, mutant rescue experiments, reciprocal interaction assays; replicated across two concurrent papers\",\n      \"pmids\": [\"15538386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ERK4 (MAPK4), a stable protein, binds endogenous MK5 and translocates MK5 to the cytoplasm. Unlike ERK3, ERK4 requires its own catalytic activity to activate MK5 (direct phosphorylation). ERK4 can dimerize/oligomerize with ERK3, enabling ERK4 to relay activation to MK5 in the context of kinase-dead ERK3.\",\n      \"method\": \"Co-immunoprecipitation, kinase-dead mutants, transfection in HEK293 cells, immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with mutant analysis, single lab, two orthogonal methods\",\n      \"pmids\": [\"16973613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PRAK activates p53 by direct phosphorylation, mediating oncogenic ras-induced senescence downstream of p38 MAPK. PRAK deficiency in mice enhances DMBA-induced skin carcinogenesis coinciding with impaired senescence induction.\",\n      \"method\": \"In vitro kinase assay, PRAK knockout mice, primary cell transformation assay, DMBA skin carcinogenesis model\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro direct phosphorylation, knockout mouse carcinogenesis model, multiple orthogonal methods\",\n      \"pmids\": [\"17254968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PKA catalytic subunit Cα interacts with MK5 (but not MK2) in vivo, increases MK5 kinase activity and phosphorylation, and induces transient nuclear export of MK5, which requires kinase activity of both Cα and MK5 and Cα nuclear entry. MK5 is required for PKA-induced F-actin rearrangement in PC12 cells.\",\n      \"method\": \"Co-immunoprecipitation, kinase assays, siRNA depletion, constitutively active MK5 expression, fluorescence microscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, siRNA rescue, multiple functional readouts, single lab\",\n      \"pmids\": [\"17947239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"14-3-3ε interacts with MK5 in vivo and in vitro, and this interaction inhibits MK5-mediated phosphorylation of HSP27, thereby disrupting F-actin polymerization and inhibiting MK5-induced cell migration.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding assay, transfection, cell migration assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP plus functional readout, single lab\",\n      \"pmids\": [\"17728103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Activation loop phosphorylation of ERK3 and ERK4 (at their SEG motif) is required for formation of stable active complexes with MK5 and for efficient cytoplasmic redistribution of ERK3/ERK4-MK5 complexes. This phosphorylation is constitutive in resting cells and can be modulated by MK5 interaction.\",\n      \"method\": \"Phospho-specific antibodies, mutagenesis of SEG motif, co-immunoprecipitation, subcellular fractionation\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis combined with Co-IP and localization assays, single lab\",\n      \"pmids\": [\"18720373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ERK4 Ser186 (in its SEG motif) is phosphorylated in vivo by an upstream kinase (not autophosphorylation); Ser186 phosphorylation is required for ERK4 to interact with, activate, and cytoplasmatically anchor MK5. MK5 binding facilitates Ser186 phosphorylation and stabilizes the ERK4-MK5 complex.\",\n      \"method\": \"Mutagenesis of Ser186, phospho-specific antibodies, co-immunoprecipitation, kinase assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — site-directed mutagenesis plus functional kinase assay, single lab\",\n      \"pmids\": [\"18248330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Distinct amino acid residues in p38α (Asp145, Leu156) versus p38β (Gly145, Val156) determine the differential subcellular localization of p38α-PRAK (nuclear) versus p38β-PRAK (cytosolic) complexes. Nuclear localization of PRAK is required for its function in inhibiting NIH3T3 cell proliferation.\",\n      \"method\": \"Chimeric and point mutants of p38α/β, immunofluorescence, nuclear import/export assays, cell proliferation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis with localization and functional readout, single lab\",\n      \"pmids\": [\"18268017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ERK3 and ERK4 contain a novel MK5-interaction motif (FRIEDE) in their L16 C-terminal extension, distinct from the classical CD domain. A single I→K substitution in FRIEDE abolishes binding, activation, and translocation of MK5 by both ERK3 and ERK4. Activation loop phosphorylation of ERK3/4 gates accessibility of the FRIEDE motif.\",\n      \"method\": \"Peptide overlay assays, mutagenesis of FRIEDE motif, co-immunoprecipitation, kinase activation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — mutagenesis defining interaction motif with multiple functional readouts (binding, activation, localization), single lab\",\n      \"pmids\": [\"19473979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MK5 interacts with HSP27 in vivo and phosphorylates HSP27 at Ser78 and Ser82 in cells. Expression of constitutively active MK5 induces F-actin rearrangement in PC12 cells, and co-expression of non-phosphorylatable Hsp27-3A abrogates this effect.\",\n      \"method\": \"Co-immunoprecipitation, phospho-specific antibodies, constitutively active MK5 expression, siRNA depletion of Hsp27, fluorescence microscopy\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with functional mutant rescue, single lab\",\n      \"pmids\": [\"19166925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PKA phosphorylates MK5 at Ser115 in vitro; PKA-induced nuclear export of MK5 requires Ser115 phosphorylation (S115A blocks PKA-induced export; S115D phosphomimetic causes cytoplasmic localization in resting cells). Mutations in Ser115 affect MK5 biological properties.\",\n      \"method\": \"In vitro kinase assay, mutagenesis of Ser115, nuclear export assay, phosphomimetic mutant analysis\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro phosphorylation with site-directed mutagenesis and functional localization readout, single lab\",\n      \"pmids\": [\"20734105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MK5 regulates translation of c-Myc by promoting expression of miR-34b and miR-34c through phosphorylation of FoxO3a, which promotes nuclear localization of FoxO3a enabling it to induce miR-34b/c expression. This establishes a MK5-FoxO3a-miR-34b/c negative feedback loop that suppresses Myc and is disrupted in colorectal cancer.\",\n      \"method\": \"siRNA kinome screen, reporter assays, FoxO3a phosphorylation assay, nuclear localization of FoxO3a by immunofluorescence, miRNA expression analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — kinome siRNA screen followed by mechanistic dissection with multiple orthogonal methods, single lab with strong evidence\",\n      \"pmids\": [\"21329882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MK5 activates FoxO3a by phosphorylation in developing B cells; this MK5-mediated phosphorylation of Foxo1 at Ser215 is required for transcriptional activation of Rag genes. MK5 is necessary and sufficient to activate Rag transcription in pro-B cells.\",\n      \"method\": \"Foxo1 mutant panel screen, in vitro and in vivo phosphorylation, B cell transformation and primary pro-B cell assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site identification by mutant panel, functional rescue in primary cells, single lab\",\n      \"pmids\": [\"23878308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The p38β-PRAK cascade mediates energy-starvation-induced suppression of mTORC1. PRAK directly phosphorylates Rheb at Ser130, impairing Rheb nucleotide-binding ability and inhibiting Rheb-mediated mTORC1 activation. This pathway operates independently of AMPK-TSC2 and AMPK-Raptor pathways.\",\n      \"method\": \"In vitro kinase assay, Rheb phosphorylation mapping, siRNA depletion, mTORC1 activity assays, cell-size measurement\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct in vitro phosphorylation with site mapping, epistasis experiments, and multiple functional readouts\",\n      \"pmids\": [\"21336308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In IGF2BP1-expressing tumor cells, inhibition of MAPK4 mRNA translation by IGF2BP1 antagonizes MK5 activation and prevents MK5-mediated HSP27 phosphorylation, which would otherwise sequester actin monomers, reducing availability of G-actin for F-actin polymerization and cell migration.\",\n      \"method\": \"Translational inhibition assay, MK5 activity measurements, HSP27 phosphorylation, F-actin/G-actin assays, cell migration assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical assays linking MAPK4-MK5-HSP27-actin axis, single lab\",\n      \"pmids\": [\"22279049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Tip60 acetylates PRAK at K364 in a manner that depends on prior phosphorylation of both Tip60 (Thr158 by p38) and PRAK by p38, inducing PRAK kinase activity. This defines a cascade: ras→p38→Tip60 acetylation→PRAK activation→oncogene-induced senescence.\",\n      \"method\": \"In vitro acetyltransferase assay, mutagenesis of Tip60-Thr158 and PRAK-K364, co-immunoprecipitation, senescence assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — biochemical reconstitution of PTM cascade with mutagenesis and functional senescence readout\",\n      \"pmids\": [\"23685072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MK5 physically interacts with Hsp40/DnaJB1 in cells via C-terminal regions of both proteins and phosphorylates Hsp40/DnaJB1 at Ser149 and/or Ser151 and Ser171 in vivo. MK5 modestly stimulates Hsp40/Hsp70 ATPase activity and enhances Hsp40/DnaJB1-mediated repression of HSF1-driven transcription.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, phospho-specific antibodies, ATPase activity assay, luciferase reporter assay\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus in vitro phosphorylation and functional assays, single lab\",\n      \"pmids\": [\"24309468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PRAK interacts with DJ-1 (via yeast two-hybrid confirmed by Co-IP) and phosphorylates DJ-1 in vitro and in vivo upon H2O2 stimulation. In PRAK-/- cells, DJ-1 translocates from nucleus to cytoplasm after H2O2, losing its ability to sequester the pro-apoptotic protein Daxx in the nucleus, leading to cell death.\",\n      \"method\": \"Yeast two-hybrid, Co-immunoprecipitation, in vitro kinase assay, immunofluorescence in PRAK+/+ vs PRAK-/- cells, Daxx localization assay\",\n      \"journal\": \"Oxidative medicine and cellular longevity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid confirmed by Co-IP and phosphorylation, functional localization in knockout cells, single lab\",\n      \"pmids\": [\"25383140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PRAK is phosphorylated by Src kinase, directing PRAK to focal adhesions. Overexpressed PRAK inhibits cell motility by phosphorylating FAK at Y861, thereby impairing FAK activation. PRAK and Src/FAK interact physically in focal adhesions.\",\n      \"method\": \"In situ kinase overlay assay, co-immunoprecipitation, phospho-specific antibodies for FAK Y861, motility assay, immunofluorescence\",\n      \"journal\": \"Journal of cancer biology & research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, journal not peer-reviewed at high tier, limited validation methods\",\n      \"pmids\": [\"26042227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PRAK interacts with RAGE (receptor for advanced glycation end-products) and Aβ treatment increases PRAK phosphorylation and PRAK-RAGE interaction. PRAK knockdown rescues mTORC1 inactivation induced by Aβ and decreases Aβ-induced autophagosome formation, placing PRAK in the RAGE-mTORC1-autophagy pathway in Alzheimer's disease models.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, mTORC1 activity assay, autophagosome quantification\",\n      \"journal\": \"Molecular neurodegeneration\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, Co-IP with functional assay, limited mechanistic validation\",\n      \"pmids\": [\"26758977\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MK5 physically interacts with YAP and counteracts CK1δ/ε-mediated YAP ubiquitination and degradation in a LATS1/2-independent manner. MK5 kinase activity is essential for protecting YAP from ubiquitin-mediated degradation and cytoplasmic retention.\",\n      \"method\": \"RNAi screen, co-immunoprecipitation, ubiquitination assay, kinase-dead MK5 mutant, xenograft model\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi screen followed by Co-IP, ubiquitination assay, and mutant analysis; single lab\",\n      \"pmids\": [\"31578200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Loss-of-function variants in MAPKAPK5 cause a developmental disorder with neurological, cardiac, and digital anomalies. Patient-derived fibroblasts lack MAPKAPK5 protein isoforms, have reduced ERK3 levels, and show impaired F-actin recovery after latrunculin B treatment, supporting a role of MAPKAPK5 in F-actin polymerization.\",\n      \"method\": \"Exome sequencing, patient-derived fibroblast functional assays (F-actin recovery after latrunculin B treatment), Western blot\",\n      \"journal\": \"Genetics in medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient-derived cells with direct functional assay, two independent families; mechanistic link to F-actin confirmed\",\n      \"pmids\": [\"33442026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PRAK deficiency abrogates lung metastases in PyMT mice and after intravenous injection of tumor cells, with no effect on primary tumor growth. Loss of PRAK leads to pronounced inhibition of HIF-1α protein synthesis, possibly due to reduced mTORC1 activities.\",\n      \"method\": \"Prak knockout mouse models, PyMT mammary tumor model, intravenous tumor injection, Western blot for HIF-1α and mTORC1 components\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockout mouse with defined metastasis phenotype and molecular mechanism, single lab\",\n      \"pmids\": [\"33741957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TLK1 phosphorylates MK5 at three residues (S160, S354, S386), resulting in MK5 activation. MK5-S354A or kinase-dead MK5 in MK5-/- MEF cells fails to restore motility compared to wild-type MK5. The TLK1-MK5 axis promotes prostate cancer cell motility and invasion.\",\n      \"method\": \"In vitro kinase assay, phospho-specific antibody for pMK5-S354, mutagenesis, MK5 knockout MEF rescue, motility assay\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-directed mutagenesis with functional rescue in knockout cells plus in vitro phosphorylation, single lab\",\n      \"pmids\": [\"35064619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ERK3-MK5 signaling promotes FoxO3 degradation by MK5-mediated direct phosphorylation of FoxO3, reducing FoxO3 association with MyoD and inhibiting myogenic differentiation. Loss of ERK3 or MK5 causes precocious myoblast differentiation; depletion of FoxO3 rescues this premature differentiation.\",\n      \"method\": \"In vitro kinase assay, genetic inactivation of ERK3 (Mapk6KD/KD mice) and MK5, C2C12 and primary myoblast differentiation assays, FoxO3 depletion rescue experiments\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro phosphorylation, multiple genetic models (kinase-dead ERK3 mice, MK5 KO), epistasis with FoxO3, replicated in multiple cell types\",\n      \"pmids\": [\"35141958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PRAK phosphorylates NRF2 at Ser558, enhancing NRF2 protein stability independent of ubiquitination. Loss of PRAK increases cellular ROS, disrupts glycolysis and PKM2-dependent STAT3 phosphorylation, and impairs Th17 cell differentiation. Prak KO mice show resistance to EAE but impaired antitumor immunity.\",\n      \"method\": \"In vitro kinase assay identifying NRF2 as MK5/PRAK substrate, Prak knockout mice, Th17 differentiation assays, ROS measurement, glycolysis assays\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct substrate identification with site mapping, knockout mouse phenotype, multiple pathway readouts, single lab\",\n      \"pmids\": [\"37126714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Septin 8 is an interaction partner and in vitro substrate of MK5; the interaction is confirmed by GST pulldown, Co-IP, and FRET. MK5 phosphorylates Ser242 and Ser271 on Septin 8 in vitro. MK5 and Septin 8 co-localize in the perinuclear area, cell protrusions, and with synaptophysin-positive vesicles.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, Co-immunoprecipitation, FRET, in vitro kinase assay, confocal microscopy\",\n      \"journal\": \"World journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal binding assays plus in vitro phosphorylation and colocalization, single lab\",\n      \"pmids\": [\"22649572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FXR1 drives retention of exon 6 in MK5 pre-mRNA, generating a long kinase-competent MK5-L isoform in HCC. MK5-L phosphorylates GSK3β, activating Wnt/β-catenin signaling and promoting HCC progression and metastasis.\",\n      \"method\": \"Alternative splicing analysis, in vitro kinase assay, GSK3β phosphorylation, Wnt/β-catenin reporter, FXR1 knockdown/overexpression, xenograft model, antisense oligonucleotide therapeutic intervention\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct substrate phosphorylation with splicing mechanism and functional in vivo validation, single lab\",\n      \"pmids\": [\"41954085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Microglial MK5 regulates the neuroinflammatory response to ischemic stroke by controlling phosphorylation of HSP27 and NF-κB. Microglia-specific MK5 knockout exacerbates neurological deficits, increases infarct volume, upregulates pro-inflammatory cytokines, and reduces HSP27 phosphorylation while increasing NF-κB phosphorylation.\",\n      \"method\": \"Microglia-specific conditional MK5 knockout, MCAO mouse model, OGD/R BV2 cell model, Western blot for pHSP27 and pNF-κB, cytokine qPCR, immunofluorescence\",\n      \"journal\": \"CNS neuroscience & therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional knockout with defined molecular mechanism (HSP27/NF-κB phosphorylation) and functional neurological readout, single lab\",\n      \"pmids\": [\"40237440\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAPKAPK5/PRAK/MK5 is a serine/threonine kinase activated downstream of both classical MAPKs (p38α/β, which phosphorylate its regulatory Thr182) and atypical MAPKs (ERK3 and ERK4, which bind MK5 via a FRIEDE motif in their C-terminal extension and translocate it to the cytoplasm), as well as PKA (which phosphorylates MK5 at Ser115 to drive nuclear export); once activated, MK5 phosphorylates a spectrum of substrates including HSP27 (regulating F-actin dynamics), p53 (mediating ras-induced senescence), Rheb-Ser130 (suppressing mTORC1 during energy starvation), FoxO3a (promoting miR-34b/c expression to suppress Myc and activating Rag transcription in B cells), NRF2-Ser558 (stabilizing NRF2 to maintain redox homeostasis in Th17 cells), FoxO3 (promoting its degradation to inhibit myogenic differentiation), and GSK3β (via a specific long MK5 splice isoform); MK5 also interacts with Hsp40/DnaJB1, Septin 8, YAP, DJ-1, and RAGE, and its subcellular localization (nuclear vs. cytoplasmic) is dynamically regulated by p38α/β docking interactions and phosphorylation, with distinct p38α versus p38β complexes targeting different compartments.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAPKAPK5 (PRAK/MK5) is a serine/threonine kinase that integrates signals from classical and atypical MAP kinase pathways to control cytoskeletal dynamics, cellular senescence, growth, and stress responses [#0, #7]. It was originally defined as a p38α/β-activated kinase whose regulatory Thr182 is phosphorylated to drive activity toward HSP27, coupling MK5 to F-actin remodeling [#0, #14]. Distinct from MK2, endogenous MK5 does not chaperone p38 or respond to canonical extracellular stresses [#2]; instead its activation and cytoplasmic anchoring are dominated by the atypical MAPKs ERK3 and ERK4, which bind MK5 through a FRIEDE motif in their C-terminal L16 extension, mutually stabilizing the partners and translocating MK5 out of the nucleus [#4, #5, #13]. MK5 subcellular distribution is further tuned by p38α versus p38β docking, which respectively retain it in the nucleus or cytoplasm, and by PKA, which phosphorylates Ser115 to drive nuclear export [#3, #12, #15]. Functionally, MK5 enforces oncogene-induced senescence by directly phosphorylating p53 downstream of a ras→p38→Tip60 acetylation cascade, with knockout mice showing enhanced carcinogenesis [#7, #20]. It additionally phosphorylates Rheb-Ser130 to suppress mTORC1 during energy starvation, FoxO transcription factors to control Myc-suppressing miR-34b/c and Rag transcription, NRF2-Ser558 to maintain redox homeostasis, and GSK3β via a long splice isoform, linking MK5 to metabolic, immune, and Wnt signaling outputs [#18, #16, #17, #30, #32]. Loss-of-function variants in MAPKAPK5 cause a developmental disorder with neurological, cardiac, and digital anomalies, with patient fibroblasts showing reduced ERK3 levels and impaired F-actin recovery [#26].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established MK5/PRAK as a p38-activated kinase and identified its regulatory phosphorylation site and a first substrate, defining where it sits in stress signaling.\",\n      \"evidence\": \"In vitro and in-gel kinase assays with Thr182 mutagenesis and Co-IP, plus parallel recombinant kinase work showing ERK/p38 activation\",\n      \"pmids\": [\"9628874\", \"9480836\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological upstream activator in vivo not resolved among p38/ERK\", \"Substrate spectrum beyond HSP27/myosin light chain peptide unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Distinguished MK5 from MK2 and showed its localization is governed by p38 docking, redefining MK5 as a distinct enzyme rather than a p38 chaperone.\",\n      \"evidence\": \"MK5 knockout fibroblasts with kinase and Co-IP assays; imaging plus NES/NLS mutants and leptomycin B\",\n      \"pmids\": [\"14560018\", \"12808055\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conflicts with founding HSP27 substrate claim left unreconciled\", \"True physiological activator still unidentified at this stage\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identified ERK3 (and later ERK4) as the atypical MAPK partners that bind, activate, and cytoplasmically anchor MK5, resolving the missing upstream activator and revealing reciprocal protein stabilization.\",\n      \"evidence\": \"Reciprocal Co-IP, siRNA, ERK3/MK5 knockout fibroblasts and embryonic-lethal mice, kinase-dead mutants, immunofluorescence\",\n      \"pmids\": [\"15577943\", \"15538386\", \"16973613\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why ERK3 acts catalysis-independently while ERK4 requires its own activity\", \"Physiological signals that engage the ERK3/4-MK5 module unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Linked MK5 to tumor suppression by showing it phosphorylates p53 to drive ras-induced senescence, and to PKA signaling controlling actin remodeling, expanding MK5 into cell-fate and cytoskeletal control.\",\n      \"evidence\": \"In vitro kinase assays, PRAK knockout mice with DMBA carcinogenesis, transformation assays; PKA Cα Co-IP, siRNA, F-actin readouts\",\n      \"pmids\": [\"17254968\", \"17947239\", \"17728103\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether p38-MK5-p53 axis operates beyond ras-driven contexts\", \"Relative contribution of nuclear vs cytoplasmic MK5 pools to each output\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the FRIEDE motif as the structural basis of ERK3/4-MK5 binding and confirmed HSP27-Ser78/82 as a cellular substrate, mechanizing both complex assembly and cytoskeletal output.\",\n      \"evidence\": \"Peptide overlay and FRIEDE mutagenesis with binding/activation/localization readouts; phospho-specific antibodies and Hsp27-3A rescue\",\n      \"pmids\": [\"19473979\", \"19166925\", \"18720373\", \"18248330\", \"18268017\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the kinase phosphorylating ERK4 SEG motif\", \"How activation-loop phosphorylation gates FRIEDE accessibility mechanistically\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected MK5 to growth and transcriptional control by identifying Rheb-Ser130 (mTORC1 suppression) and FoxO3a/Foxo1 (miR-34b/c-Myc loop, Rag activation) as direct substrates.\",\n      \"evidence\": \"In vitro kinase assays with site mapping, kinome/mutant screens, reporter assays, epistasis, and primary B-cell rescue\",\n      \"pmids\": [\"21336308\", \"21329882\", \"23878308\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a single kinase selects between cytoskeletal, senescence, and transcriptional substrates\", \"In vivo significance of MK5-Rheb axis across tissues\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Resolved the activation logic of MK5 in senescence as a PTM cascade (p38-dependent Tip60 acetylation of PRAK-K364) and added Hsp40/DnaJB1 as a substrate, refining the activation and chaperone interface.\",\n      \"evidence\": \"In vitro acetyltransferase and kinase assays with Tip60-T158/PRAK-K364 mutagenesis, Co-IP, senescence and ATPase/reporter assays\",\n      \"pmids\": [\"23685072\", \"24309468\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality of acetylation-dependent activation beyond ras senescence\", \"Functional consequence of Hsp40 phosphorylation in vivo\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Extended MK5 into oxidative-stress and motility control through interactions with DJ-1, Septin 8, and Src/FAK, implicating it in apoptosis regulation and focal-adhesion dynamics.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, FRET, in vitro phosphorylation, knockout-cell localization assays; Src/FAK overlay and motility assays\",\n      \"pmids\": [\"25383140\", \"22649572\", \"26042227\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Src/FAK axis rests on a single low-tier study without independent confirmation\", \"Physiological stimuli engaging DJ-1 and Septin 8 phosphorylation unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Implicated MK5 in Hippo and metastasis biology by showing it protects YAP from CK1-mediated degradation and is required for HIF-1α synthesis and lung metastasis.\",\n      \"evidence\": \"RNAi screen, Co-IP, ubiquitination assays, kinase-dead mutant, xenografts; PRAK knockout PyMT and IV-injection metastasis models\",\n      \"pmids\": [\"31578200\", \"33741957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct YAP phosphorylation site not defined\", \"Mechanistic link between MK5, mTORC1, and HIF-1α translation incomplete\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established MAPKAPK5 as a disease gene, with loss-of-function variants causing a multisystem developmental disorder and confirming the F-actin role in patient cells.\",\n      \"evidence\": \"Exome sequencing in two families, patient fibroblast F-actin recovery assays, Western blot for MK5 isoforms and ERK3\",\n      \"pmids\": [\"33442026\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which substrate pathways drive the cardiac and digital phenotypes\", \"Genotype-phenotype correlation across variant types\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Broadened the MK5 substrate repertoire across immunity, neuroinflammation, alternative upstream kinases, and cancer-specific splice isoforms, showing context-dependent rewiring of the kinase.\",\n      \"evidence\": \"In vitro kinase assays and site mapping (NRF2-Ser558, GSK3β), Prak/MK5 knockout and conditional knockout mice (Th17/EAE, MCAO stroke), TLK1 phosphorylation rescue, FXR1-driven exon-6 splicing with ASO intervention\",\n      \"pmids\": [\"37126714\", \"40237440\", \"35064619\", \"35141958\", \"41954085\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How distinct upstream kinases (TLK1, Src, PKA, p38, ERK3/4) are selected in each context\", \"Whether splice-isoform-specific substrate selectivity generalizes beyond HCC\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MK5 achieves substrate selectivity among its many targets and which upstream activator dominates in a given physiological setting remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model linking activator identity to substrate output\", \"Structural basis of isoform- and compartment-specific substrate choice unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 7, 14, 16, 18, 21, 22, 28, 29, 30, 31, 32]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 7, 18, 30]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 5, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 12, 16]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3, 4, 5, 6, 12]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [14, 19, 23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 4, 8, 18, 25]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [7, 20, 22]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [18, 22, 30]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [7, 20, 12]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [17, 30]}\n    ],\n    \"complexes\": [\n      \"ERK3-MK5 complex\",\n      \"ERK4-MK5 complex\",\n      \"p38-MK5 complex\"\n    ],\n    \"partners\": [\n      \"MAPK6\",\n      \"MAPK4\",\n      \"MAPK14\",\n      \"PRKACA\",\n      \"YWHAE\",\n      \"DNAJB1\",\n      \"PARK7\",\n      \"SEPT8\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}