{"gene":"MAPK9","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":1994,"finding":"JNK2 (55 kD form of JNK) was molecularly cloned and shown to phosphorylate c-Jun at its amino-terminal activation sites. JNK2 binds c-Jun approximately 25 times more efficiently than JNK1, resulting in a lower Km toward c-Jun. A small beta-strand-like region near the catalytic pocket of JNK2 was identified as the structural basis for this differential substrate recognition, serving as a docking site that increases the effective concentration of c-Jun near JNK2.","method":"Molecular cloning, in vitro kinase assays, Km determination, structural modeling and mutagenesis to map the specificity-determining region","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assay with quantitative Km measurement plus domain mutagenesis to identify the docking region; foundational mechanistic paper","pmids":["8001819"],"is_preprint":false},{"year":1994,"finding":"SEK1 (SAPK/ERK kinase-1) was identified as a direct upstream activator of SAPKs/JNKs in vitro and in vivo. SEK1 is structurally related to MAP kinase kinases (MEKs). A kinase-inactive SEK1 mutant blocks SAPK activation by extracellular stimuli without interfering with the MAPK/ERK pathway, placing SEK1 immediately upstream of SAPK/JNK in a distinct stress-activated signaling cascade that couples cellular stress to c-Jun phosphorylation.","method":"In vitro kinase assay, dominant-negative mutant expression, in vivo pathway epistasis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution plus dominant-negative epistasis; replicated in multiple studies","pmids":["7997269"],"is_preprint":false},{"year":1996,"finding":"Ceramide initiates apoptosis through the SAPK/JNK cascade, providing evidence that ceramide-generated second messenger signals are integrated with cytokine- and stress-activated apoptotic pathways via SAPK/JNK activation.","method":"Cell-based apoptosis assays with ceramide treatment, SAPK/JNK activity measurements, pharmacological and genetic inhibition of SAPK pathway","journal":"Nature","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based functional assays with pathway inhibition; single lab but mechanistically defined","pmids":["8598911"],"is_preprint":false},{"year":1996,"finding":"MLK-3 (Mixed Lineage Kinase-3) activates SAPK/JNK through direct phosphorylation of SEK1 in vitro, and co-precipitates with SEK1, placing MLK-3 as an upstream MAPKKK in the SAPK/JNK cascade downstream of Ste20-like kinases.","method":"In vitro kinase assay (immunoprecipitated MLK-3 phosphorylating SEK1), co-precipitation, dominant-negative epistasis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro phosphorylation reconstitution plus co-precipitation and epistasis; multiple orthogonal methods","pmids":["9003778"],"is_preprint":false},{"year":1997,"finding":"TNF-R1-mediated activation of SAPK/JNK occurs through a noncytotoxic TRAF2-dependent pathway. TRAF2 is both sufficient and necessary for SAPK activation by TNF-R1, and this pathway is distinct from the FADD-dependent apoptotic pathway.","method":"Dominant-negative TRAF2 and FADD mutant expression, SAPK activity assays, epistasis","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with dominant-negatives in defined pathway; replicated in multiple contexts","pmids":["8985011"],"is_preprint":false},{"year":1997,"finding":"MKK7 was identified as a novel SAPK/JNK-specific kinase (MAPKK). Unlike SEK1/MKK4 which activates both SAPK/JNK and p38, MKK7 is specific for the SAPK/JNK subgroup. MKK7 is a major SAPK/JNK-activating kinase in osmotically shocked cells and a major activator of SAPK/JNK in the TNF-alpha-stimulated pathway.","method":"Molecular cloning, immunochemical identification, in vitro kinase specificity assays, column fractionation, AP-1 reporter assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase specificity reconstitution with multiple substrates; isoform specificity defined biochemically","pmids":["9384583"],"is_preprint":false},{"year":1998,"finding":"Germinal center kinase (GCK) couples TRAF2 to MEKK1 and thereby to SAPK/JNK activation downstream of TNF-R1. GCK interacts in vivo with TRAF2 and MEKK1. Separately, RIP associates with an endogenous MAPKKK upstream of the p38 pathway, demonstrating two distinct proximal kinase branches downstream of TRAF2.","method":"Co-immunoprecipitation (in vivo interaction), in vitro kinase assays, epistasis by overexpression","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and in vitro kinase assay; single lab","pmids":["9712898"],"is_preprint":false},{"year":1999,"finding":"JNK1 and JNK2 together are required for region-specific apoptosis during early brain development. Jnk1/Jnk2 double-knockout mice are embryonic lethal with severe dysregulation of apoptosis in the brain: reduced cell death in hindbrain neuroepithelium prior to neural tube closure and increased apoptosis with caspase activation in the forebrain.","method":"Knockout mouse genetics, histology, caspase activity assays, apoptosis quantification","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — double-knockout mouse model with specific phenotypic readouts; replicated independently","pmids":["10230788"],"is_preprint":false},{"year":1999,"finding":"JNK2 is essential for efficient T-cell activation: Jnk2-/- mice show defective peripheral T-cell proliferation and reduced IL-2, IL-4, and IFN-gamma production after anti-CD3 stimulation. JNK2 is also required for anti-CD3-induced apoptosis of immature (CD4+CD8+) thymocytes but not for apoptosis induced by anti-Fas, dexamethasone, or UV-C. B-cell activation is normal in JNK2-deficient mice.","method":"Jnk2 knockout mice, T-cell proliferation assays, cytokine production assays (IL-2, IL-4, IFN-gamma), apoptosis assays with multiple stimuli","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout mice with multiple orthogonal functional assays; stimulus-specific phenotype defined","pmids":["10021384"],"is_preprint":false},{"year":1999,"finding":"Jnk1/Jnk2 double-knockout mice die around embryonic day 11 with open neural tube (exencephaly) at hindbrain level and altered apoptosis: reduced apoptosis in hindbrain neuroepithelium at E9.25, then dramatically increased cell death at E10.5 in both hindbrain and forebrain. About 25% of jnk1-/-jnk2+/- fetuses display exencephaly, while jnk1+/-jnk2-/- mice are viable, indicating dose-dependency.","method":"Knockout mouse genetics (single and compound), embryological analysis, TUNEL assay","journal":"Mechanisms of development","confidence":"High","confidence_rationale":"Tier 2 / Strong — compound knockout mouse with multiple genotypes and temporal developmental analysis","pmids":["10559486"],"is_preprint":false},{"year":2000,"finding":"In response to ionizing radiation, SAPK/JNK translocates to mitochondria and associates with the anti-apoptotic protein Bcl-x(L). SAPK phosphorylates Bcl-x(L) on Thr-47 and Thr-115 in vitro and in vivo. A Bcl-x(L) mutant with both threonines substituted by alanines (Ala-47, Ala-115) is a more potent inhibitor of ionizing radiation-induced apoptosis than wild-type Bcl-x(L), demonstrating that SAPK-mediated phosphorylation of Bcl-x(L) attenuates its anti-apoptotic function.","method":"Subcellular fractionation/translocation assay, co-immunoprecipitation, in vitro and in vivo kinase assay, site-directed mutagenesis of Bcl-x(L), apoptosis assay with mutant rescue","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assay with site identification plus mutagenesis functional rescue; multiple orthogonal methods","pmids":["10617621"],"is_preprint":false},{"year":2001,"finding":"MKP-7, a novel dual-specificity phosphatase, binds to and inactivates SAPK/JNK and p38alpha/beta MAPKs but not ERK. MKP-7 is predominantly cytoplasmic, distinguishing it from hVH5 (which is nuclear and cytoplasmic). MKP-7 shows isoform specificity within the p38 family, inactivating p38alpha and p38beta but not p38gamma or delta.","method":"Molecular cloning, in vitro phosphatase activity assay, co-immunoprecipitation/binding assay, subcellular localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with substrate specificity determination and subcellular localization; single lab with multiple methods","pmids":["11359773"],"is_preprint":false},{"year":2002,"finding":"PKCdelta is required for SAPK/JNK activation in response to DNA damage (araC and other genotoxins). PKCdelta activates SAPK through an MKK7-dependent, SEK1-independent mechanism. The pathway is: Lyn tyrosine kinase → PKCdelta → MEKK1 → MKK7 → SAPK.","method":"Pharmacological inhibition (rottlerin), kinase-inactive PKCdelta mutant, siRNA knockdown, co-expression epistasis assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple inhibition approaches (pharmacological, dominant-negative, siRNA) defining pathway order; single lab","pmids":["12377781"],"is_preprint":false},{"year":2003,"finding":"SAPK/JNK directly phosphorylates the cdc2 regulator cdc25c on serine 168 (S168) in vitro. This phosphorylation inhibits cdc25c phosphatase activity in cells. A S168A cdc25c mutant reverses SAPK-induced inhibition of cdc2/cyclin B kinase activity, establishing a novel mechanism by which SAPK regulates the G2/M transition through inhibitory phosphorylation of cdc25c.","method":"In vitro kinase assay (direct phosphorylation of cdc25c), site-directed mutagenesis (S168A), phospho-specific antibody, cdc2/cyclin B kinase activity assay, mutant rescue","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with site identification, mutagenesis rescue, and in vivo phosphorylation confirmation; multiple orthogonal methods","pmids":["12742231"],"is_preprint":false},{"year":2004,"finding":"JNK2 and JNK1 have distinct and opposing roles in regulating c-Jun and cell proliferation. In unstimulated cells, JNK2 is preferentially bound to c-Jun and promotes c-Jun degradation, making JNK2 a negative regulator of c-Jun stability and cellular proliferation. In contrast, JNK1 becomes the major c-Jun interacting kinase after cell stimulation and promotes c-Jun phosphorylation and stability. Jnk2-/- fibroblasts exhibit elevated c-Jun phosphorylation and stability with accelerated G1/S transition; Jnk1-/- cells show the inverse. Re-expression of JNK2 in Jnk2-/- cells reverses the phenotype.","method":"Jnk1 and Jnk2 knockout fibroblasts and erythroblasts, cell cycle analysis (BrdU incorporation), co-immunoprecipitation, c-Jun stability assays, rescue by re-expression","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal knockout analysis with re-expression rescue, co-IP, and multiple cell types; mechanistic model well-supported","pmids":["15350216"],"is_preprint":false},{"year":2004,"finding":"JNK2 is required for scavenger receptor A (SR-A)-mediated foam cell formation in atherosclerosis. JNK2-deficient macrophages display suppressed foam cell formation due to defective uptake and degradation of modified lipoproteins. SR-A phosphorylation is markedly decreased in JNK2-deficient macrophages. Macrophage-restricted deletion of JNK2 is sufficient to decrease atherogenesis in ApoE-/- mice.","method":"Jnk2 knockout and macrophage-specific conditional knockout in ApoE-/- mice, foam cell formation assays, SR-A phosphorylation assay, lipoprotein uptake assays","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-specific conditional knockout plus biochemical phosphorylation assay; multiple orthogonal methods and in vivo validation","pmids":["15567863"],"is_preprint":false},{"year":2004,"finding":"Inhibition of JNK2 (but not JNK1) by dominant-negative mutant, pharmacological inhibitor, or RNAi causes accumulation of mammalian cells with 4N DNA content. Cells progress normally to metaphase but exhibit defects in central spindle formation and chromosome segregation during anaphase, leading to polyploidy. CDK1 activity, cyclin B1, and PLK1 turnover remain intact, indicating JNK2 regulates anaphase through a CDK1/cyclin B1-independent mechanism.","method":"Dominant-negative JNK2 expression, pharmacological JNK inhibition, RNAi, flow cytometry (DNA content), immunofluorescence microscopy of mitotic cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — three independent inhibition methods converging on the same phenotype; single lab","pmids":["15262983"],"is_preprint":false},{"year":2005,"finding":"Disruption of Mapk9 (encoding JNK2) in non-obese diabetic mice decreases destructive insulitis and reduces progression to type 1 diabetes. CD4+ T cells from JNK2-deficient NOD mice produce less IFN-gamma but increased IL-4 and IL-5, indicating JNK2 controls Th1/Th2 balance of the immune response.","method":"Jnk2 (Mapk9) knockout in NOD mice, insulitis scoring, diabetes incidence monitoring, cytokine production assays (ELISA/intracellular staining)","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean in vivo knockout with multiple immunological readouts; specific isoform function established","pmids":["15867147"],"is_preprint":false},{"year":2005,"finding":"During glucose deprivation, SEK1 phosphorylates JNK2 on Tyr-185 after being activated by ASK1 (via JIP3 scaffold). Phosphorylated JNK2 then binds JIP1 scaffold, whereupon Thr-183 of JNK2 is phosphorylated. JNK2 phosphorylates JIP1 on Thr-103, causing dissociation of Akt1 from JIP1. Released Akt1 then inhibits SEK1 and ASK1 through phosphorylation, forming a negative feedback loop.","method":"Co-immunoprecipitation, in vitro kinase assay, site-directed mutagenesis (phosphorylation sites), siRNA knockdown, overexpression","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple co-IP and in vitro kinase assays with defined phosphorylation sites; single lab","pmids":["15911620"],"is_preprint":false},{"year":2006,"finding":"Using a chemical genetic approach, both JNK1 and JNK2 are shown to be positive regulators of cJun expression and cell proliferation. The previously reported opposing phenotypes of Jnk1 and Jnk2 knockout mice are explained by competition between the two isoforms rather than inherently opposite activities.","method":"Chemical genetic (analog-sensitive kinase) approach, Jnk1 and Jnk2 knockout fibroblasts, c-Jun expression/phosphorylation assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — chemical genetics allows isoform-specific inhibition; orthogonal to prior knockout data; mechanistically resolves contradictory findings","pmids":["16973441"],"is_preprint":false},{"year":2006,"finding":"CARMA1 and Bcl10 selectively regulate JNK2 (but not JNK1) in the TCR-signaling pathway. Bcl10 inducibly associates with JNK2 and functions as a JIP-like scaffold to assemble JNK2, MKK7, and TAK1. This CARMA1/Bcl10-mediated JNK2 activation regulates c-Jun protein levels after TCR stimulation.","method":"Knockout mice (CARMA1-/-, Bcl10-/-), co-immunoprecipitation, isoform-selective JNK assays, c-Jun expression analysis","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP plus genetic knockouts define the isoform-selective scaffold complex; multiple methods","pmids":["17189706"],"is_preprint":false},{"year":2007,"finding":"JNK1 and JNK2 cooperatively phosphorylate p53 at Ser6 to induce apoptosis downstream of FDH. JNK2 (but not JNK1) physically associates with p53 by pulldown assay. JNK1 phosphorylates JNK2 before JNK2 directly phosphorylates p53 at Ser6, defining a sequential JNK1→JNK2→p53 signaling mechanism.","method":"siRNA knockdown of JNK1 and JNK2, pharmacological JNK inhibition (SP600125), p53-specific pulldown assay, phospho-specific assays, rescue by overexpression","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pulldown interaction plus isoform-specific siRNA knockdown with phosphorylation site evidence; single lab","pmids":["17525747"],"is_preprint":false},{"year":2008,"finding":"JNK2 regulates SIRT1 protein stability through phosphorylation at serine 27. RNAi-mediated depletion of JNK2 reduced the half-life of SIRT1 from >9 h to <2 h, correlating with loss of SIRT1 phosphorylation at Ser27. Depletion of JNK1 had no effect on SIRT1 stability. Phosphorylation at Ser47 showed no correlation with stability.","method":"RNAi knockdown of JNK1 and JNK2, SIRT1 protein half-life measurement (pulse-chase), phosphorylation site-specific analysis","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isoform-specific RNAi with half-life quantitation and phosphorylation site correlation; single lab","pmids":["18838864"],"is_preprint":false},{"year":2009,"finding":"JNK2 inhibits hepatocyte cell death by blocking the mitochondrial death pathway. jnk2 knockdown in high-fat diet-fed mice increased liver injury in concert with increased expression of pro-apoptotic Bcl-2 family members Bim and Bax, with increased injury resulting in part from Bim-dependent activation of the mitochondrial death pathway. This is mechanistically distinct from JNK1, which promotes steatosis.","method":"Antisense oligonucleotide knockdown of jnk1 and jnk2 in vivo, liver injury assays, Bcl-2 family member expression analysis, genetic epistasis with Bim","journal":"Hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo isoform-specific knockdown with pathway epistasis; single lab","pmids":["19053047"],"is_preprint":false},{"year":2009,"finding":"JNK2 promotes degradation of ABCG1 (ATP-binding cassette transporter G1) through serine phosphorylation, leading to proteasomal degradation of the transporter and reduced cholesterol efflux. JNK2-deficient (but not JNK1-deficient) macrophages are resistant to 12S-HETE-mediated ABCG1 protein downregulation and show increased cholesterol efflux.","method":"JNK1, JNK2, and MKK3 knockout macrophages, pharmacological inhibition, dominant-negative constructs, proteasome inhibitor rescue, cholesterol efflux assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isoform-specific knockout macrophages with functional efflux assay and mechanistic rescue; single lab","pmids":["19713213"],"is_preprint":false},{"year":2009,"finding":"JNK2 suppresses a basal JNK1/c-Jun/Bcl-3 apoptotic network in cancer cells. Silencing JNK2 by RNAi results in JNK1-dependent apoptosis of cancer cells via upregulation of hypo-phosphorylated c-Jun, which auto-regulates its own expression and suppresses Bcl-3 (an IκB protein), leading to basal apoptosis via components of the TNFα response pathway.","method":"Combinatorial RNAi plus gene knockout, phosphorylation mutant expression, chromatin immunoprecipitation, apoptosis assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — combinatorial RNAi/knockout with ChIP and mechanistic follow-up; single lab","pmids":["19806201"],"is_preprint":false},{"year":2009,"finding":"Activated JNK2 increases GSK3beta activity and inhibits beta-catenin expression and transcriptional activity. JNK2-mediated beta-catenin downregulation is blocked by proteasome inhibitor MG132 and GSK3beta inhibitor LiCl, and by GSK3beta phosphorylation site mutations (Ser33/Ser37) in beta-catenin. Physical interaction among JNK2, beta-catenin, and GSK3beta was demonstrated by co-immunoprecipitation, two-hybrid assay, and confocal microscopy. JNK2-/- mice show elevated beta-catenin and increased GSK3beta phosphorylation in intestinal epithelial cells.","method":"In vitro JNK2 activation, GSK3beta activity assay, proteasome/GSK3beta inhibitor rescue, site-directed mutagenesis of beta-catenin, co-IP, mammalian two-hybrid assay, confocal co-localization, JNK2-/- mice","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal interaction methods plus in vivo knockout; single lab","pmids":["19675674"],"is_preprint":false},{"year":2011,"finding":"JNK2 promotes mammary cancer cell migration through inhibition of EPS8 (epidermal growth factor substrate 8) expression. In jnk2-/- mammary tumors, EPS8 expression is higher. Absence of JNK2 reduces cell migration that is rescued by EPS8 knockdown. JNK2 enhances formation of the EPS8-Abi-1-Sos-1 complex to augment EGFR activation of Akt and ERK; absence of JNK2 promotes EPS8/RN-Tre association to inhibit EGFR endocytic trafficking.","method":"Jnk2 knockout mice and mammary tumor cells, co-immunoprecipitation, EPS8 knockdown rescue, migration assays, EGFR trafficking assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo knockout with mechanistic rescue by EPS8 knockdown and co-IP; single lab","pmids":["21357683"],"is_preprint":false},{"year":2011,"finding":"JNK2-selective peptide inhibitors (JIP10-Δ-TAT(i) and JIP10-Δ-R9) inhibit JNK2 with IC50 ~90 nM and 10-fold selectivity over JNK1 and JNK3. These inhibitors block migration of PyVMT cancer cells in a JNK2-dependent manner: they inhibit migration of jnk2+/+ cells and jnk2-/- cells re-expressing GFP-JNK2, but not jnk2-/- cells alone.","method":"In vitro kinase assay (IC50 determination), cell-based JNK and c-Jun phosphorylation assays, JNK2 knockout cell migration assays, GFP-JNK2 rescue","journal":"ACS chemical biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with selectivity profiling plus cell-based rescue; single lab","pmids":["21438496"],"is_preprint":false},{"year":2012,"finding":"JNK2 and JNK3 are the major JNK isoforms activated in retinal ganglion cell (RGC) axons immediately after injury. Combined deficiency of Jnk2 and Jnk3 provides robust long-term protection against axonal injury-induced RGC death and prevents JUN phosphorylation and BRN3B downregulation. JNK2 and JNK3 but not JNK1 are activated in injured axons.","method":"Jnk isoform-specific knockout mice (single and double), axonal injury model (optic nerve crush), RGC survival counting, JUN phosphorylation and BRN3B marker analysis","journal":"Neurobiology of disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — isoform-specific single and double knockouts with multiple readouts; long-term survival data","pmids":["22353563"],"is_preprint":false},{"year":2012,"finding":"JNK2 is activated during ER stress and promotes cell survival by regulating the unfolded protein response (UPR). Silencing or pharmacological inhibition of JNK2 delays BiP upregulation, causes earlier/greater CHOP expression, and leads to p62 accumulation, acidic compartment accumulation, caspase-3 activation, and apoptosis. JNK2 prevents pathological accumulation of the acidic compartment during autophagic flux.","method":"Pharmacological inhibition, siRNA silencing of JNK2, UPR marker analysis (BiP, CHOP), autophagy marker (p62), caspase-3 activation, lysosomal assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and siRNA inhibition with multiple pathway readouts; single lab","pmids":["23171849"],"is_preprint":false},{"year":2012,"finding":"EGFR-inhibition by cetuximab induces JNK2 phosphorylation through JIP-4 (JNK-interacting protein 4), identified by immunoprecipitation-mass spectrometry. This JIP-4/JNK2 signaling bypass attenuates cetuximab-mediated radiosensitization; knockdown of JIP-4 or JNK2 enhances cetuximab efficacy and tumor cell radiosensitivity.","method":"Phosphoproteome arrays, immunoprecipitation-mass spectrometry, JIP-4 and JNK2 knockdown, clonogenic survival assays, 3D cell culture and xenograft models","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — IP-MS identification with functional siRNA validation; single lab","pmids":["23074283"],"is_preprint":false},{"year":2014,"finding":"MAVS specifically activates JNK2 (but not JNK1 or other MAP kinases) during viral infection via a MAVS-MKK7-JNK2 signaling axis. MAVS recruits MKK7 onto mitochondria via its 3D domain, which subsequently phosphorylates JNK2 to activate apoptosis. Jnk2-/- cells (but not Jnk1-/- cells) and Mkk7-/- cells fail to initiate virus-induced apoptosis. Jnk2-/- mice show marked inflammatory injury in lung and liver after viral challenge.","method":"Jnk1, Jnk2, Mkk7 knockout cells and mice, MAVS domain mapping, co-immunoprecipitation of MAVS with MKK7, viral infection apoptosis assays, in vivo challenge model","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple knockout cell lines and mice, domain-mapping co-IP, isoform-specific functional readouts; multiple orthogonal methods","pmids":["24651600"],"is_preprint":false},{"year":2014,"finding":"JNK2 (but not JNK1) specifically activates pro-survival autophagy in response to palmitic acid in hepatocytes. Specific knockdown of JNK2 suppresses PA-induced autophagy and enhances pro-apoptotic activity, while JNK1 knockdown has the converse effect (promoting lipoapoptosis when JNK2 is absent).","method":"Isoform-specific siRNA knockdown of JNK1 and JNK2, autophagy markers (LC3-II, Beclin1, Atg5), apoptosis assays (Annexin V, PARP cleavage), pharmacological JNK inhibition","journal":"Acta pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isoform-selective knockdown with multiple autophagy/apoptosis readouts; single lab","pmids":["24608675"],"is_preprint":false},{"year":2015,"finding":"JNK2 has a crucial role in G2-specific Golgi stack separation through direct phosphorylation of GRASP65 (also known as GORASP1) at Ser277. Inhibition of JNK2 by RNAi or three unrelated JNK inhibitors causes a potent G2 cell cycle block. JNK activity becomes dispensable for mitotic entry if the Golgi complex is disassembled by brefeldin A or GRASP65 depletion. FRAP demonstrates JNK is required for cleavage of tubules connecting Golgi stacks.","method":"RNAi, pharmacological JNK inhibition (three inhibitors), cell cycle analysis, GRASP65 site-directed mutagenesis (Ser277), brefeldin A treatment, FRAP microscopy","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct phosphorylation site identification combined with three independent inhibitor approaches, FRAP, and epistatic rescue by Golgi disassembly","pmids":["25948586"],"is_preprint":false},{"year":2015,"finding":"X-ray crystallography of JNK2/3 complexed with aminopyrazole inhibitors, combined with site-directed mutagenesis, identified residue L144 in JNK3 as a key determinant of isoform selectivity for JNK2/3 over JNK1. JNK2/3-selective inhibitors protected human dopaminergic neurons against 6-OHDA-induced ROS generation and mitochondrial membrane potential depolarization.","method":"X-ray crystallography, site-directed mutagenesis (L144), in vitro kinase selectivity assays (IC50), ROS measurement, mitochondrial membrane potential assay in dopaminergic neurons","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus mutagenesis validation plus functional consequence; multiple orthogonal methods in single study","pmids":["25623238"],"is_preprint":false},{"year":2016,"finding":"JNK2 activates PHD1 (prolyl hydroxylase 1) in docetaxel-treated cancer cells under hypoxia, leading to PHD1-mediated hydroxylation and subsequent proteasomal degradation of HIF-1α. JNK2 knockdown by siRNA blocks docetaxel-induced HIF-1α degradation and cancer cell death by inhibiting PHD1 activation.","method":"siRNA knockdown of JNK2 and PHD1, proteasome inhibitor rescue, luciferase HIF-1 reporter assay, xenograft tumor model","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA epistasis between JNK2 and PHD1 with functional HIF-1α readout and in vivo tumor model; single lab","pmids":["27263528"],"is_preprint":false},{"year":2018,"finding":"JNK2 activates CaMKII (Ca2+/calmodulin-dependent kinase II) in aged atria, which in turn upregulates diastolic sarcoplasmic reticulum Ca2+ leak via RyR2 channels, leading to aberrant intracellular Ca2+ waves and enhanced atrial fibrillation propensity. This JNK2-CaMKII-RyR2 proarrhythmic pathway is absent in young atria and is eliminated by JNK2 ablation or CaMKII inhibition.","method":"Transgenic mouse models (JNK2 ablation), electrophysiology, Ca2+ imaging, biochemical CaMKII activation assays, human donor heart studies, JNK2-specific inhibition","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Strong — transgenic mouse models plus pharmacological validation plus human tissue confirmation; multiple orthogonal methods replicated in vivo and ex vivo","pmids":["29352041"],"is_preprint":false},{"year":2018,"finding":"JNK2 activation up-regulates CaMKIIδ expression in the aged atrium at the transcriptional level through the downstream transcription factor c-jun. JNK2 (but not JNK1) activation increases CaMKIIδ mRNA and protein. Increased c-jun phosphorylation and c-jun binding to the CaMKIIδ promoter (shown by ChIP) is required; JNK2 siRNA or c-jun siRNA knockdown completely reverses this.","method":"AdMKK7D-JNK2 vs AdMKK7D-JNK1 overexpression, JNK2-specific inhibitors, dominant-negative JNK2, chromatin immunoprecipitation (ChIP), CaMKIIδ promoter-luciferase assay, siRNA knockdown","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 / Strong — isoform-specific overexpression and knockdown, ChIP, and promoter assays; multiple orthogonal methods; validated in human and mouse tissue","pmids":["29360953"],"is_preprint":false},{"year":2020,"finding":"JNK2 (but not JNK1) increases SERCA2 (SR Ca2+-ATPase) activity and consequently elevates SR Ca2+ content load. JNK2 associates with and phosphorylates SERCA2 protein. JNK2 increases SERCA2-ATPase maximal rate without altering Ca2+ affinity. This JNK2-driven SERCA2 activation is CaMKII-independent and, combined with JNK2-CaMKII-driven SR Ca2+ leak, exacerbates arrhythmic SR Ca2+ dynamics.","method":"Confocal Ca2+ imaging, biochemical co-immunoprecipitation and phosphorylation assays, ATPase activity assay, dual Ca2+/voltage optical mapping, genetic models (JNK2 ablation), CaMKII inhibition","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct phosphorylation/association demonstrated, ATPase activity reconstitution, isoform-specific genetic ablation, multiple orthogonal methods; replicated from prior work in same system","pmids":["33334123"],"is_preprint":false}],"current_model":"MAPK9/JNK2 is a stress-activated serine/threonine kinase that phosphorylates substrates including c-Jun (via a dedicated docking region conferring ~25× higher affinity than JNK1), Bcl-x(L) (Thr-47/Thr-115), GRASP65 (Ser277), SIRT1 (Ser27), cdc25c (Ser168), and SERCA2, functioning downstream of the MKK4/MKK7–MAPKKK cascade; in unstimulated cells JNK2 preferentially binds and degrades c-Jun (opposing JNK1), making it a context-dependent negative regulator of proliferation, while selective upstream scaffolds (CARMA1/Bcl10, MAVS/MKK7) and downstream substrates explain its isoform-specific roles in T-cell activation, antiviral apoptosis, foam cell formation via SR-A phosphorylation, Golgi G2/M checkpoint via GRASP65, and cardiac arrhythmogenesis via CaMKII activation and SERCA2 enhancement."},"narrative":{"mechanistic_narrative":"MAPK9/JNK2 is a stress-activated serine/threonine protein kinase that couples extracellular and intracellular stress signals to phosphorylation of substrates governing transcription, apoptosis, cell-cycle progression, and metabolism [PMID:8001819, PMID:15350216]. It acts as the terminal kinase of a defined MAPKKK→MKK4(SEK1)/MKK7→JNK cascade, in which upstream MAPKKKs such as MLK-3 and MEKK1 (engaged via GCK and TRAF2 downstream of TNF-R1) feed into SEK1/MKK7, with MKK7 being a JNK-specific activator that predominates in TNFα- and osmotic-stress signaling [PMID:7997269, PMID:9003778, PMID:9384583, PMID:9712898, PMID:8985011]. JNK2 was originally distinguished from JNK1 by a beta-strand docking region near its catalytic pocket that binds c-Jun ~25-fold more efficiently, lowering its Km for this substrate [PMID:8001819]; isoform-specific scaffolds then route JNK2 to discrete biological programs, including CARMA1/Bcl10-assembled JNK2–MKK7–TAK1 complexes in TCR signaling and a MAVS–MKK7–JNK2 mitochondrial axis driving antiviral apoptosis [PMID:17189706, PMID:24651600]. A central theme is JNK2's isoform-distinct and often opposing relationship to JNK1: in unstimulated cells JNK2 preferentially binds c-Jun and promotes its degradation, acting as a negative regulator of c-Jun stability and proliferation, with the apparent opposition to JNK1 reflecting competition between the isoforms [PMID:15350216, PMID:16973441]. JNK2 directly phosphorylates a broad substrate set—Bcl-x(L) at Thr-47/Thr-115 to attenuate its anti-apoptotic activity, cdc25c at Ser168 to regulate the G2/M transition, GRASP65/GORASP1 at Ser277 to drive G2-specific Golgi stack separation, SIRT1 at Ser27 to control its stability, and SERCA2 to enhance its ATPase activity [PMID:10617621, PMID:12742231, PMID:25948586, PMID:18838864, PMID:33334123]. Through these activities JNK2 controls developmental apoptosis, T-cell activation and Th1/Th2 balance, macrophage foam-cell formation via scavenger-receptor A phosphorylation, and atrial arrhythmogenesis via a JNK2–CaMKII–RyR2 pathway in which JNK2 also transcriptionally upregulates CaMKIIδ through c-Jun [PMID:10230788, PMID:10021384, PMID:15867147, PMID:15567863, PMID:29352041, PMID:29360953].","teleology":[{"year":1994,"claim":"Established JNK2 as a distinct c-Jun kinase and defined the structural basis for its substrate selectivity, explaining why JNK2 is a more efficient c-Jun kinase than JNK1.","evidence":"Molecular cloning, in vitro kinase assays with Km determination, and mutagenesis mapping of the docking region","pmids":["8001819"],"confidence":"High","gaps":["Cellular consequences of differential c-Jun binding not addressed","Other physiological substrates not yet known"]},{"year":1994,"claim":"Placed JNK2 in a dedicated stress-activated cascade by identifying SEK1 as a direct upstream activating kinase distinct from the ERK pathway.","evidence":"In vitro kinase assay plus dominant-negative epistasis in cells","pmids":["7997269"],"confidence":"High","gaps":["Upstream MAPKKKs not yet defined","Did not distinguish JNK1 vs JNK2 specificity of SEK1"]},{"year":1996,"claim":"Extended the cascade upstream and connected it to physiology by identifying MLK-3 as a MAPKKK acting through SEK1 and by linking ceramide-initiated apoptosis to the SAPK/JNK pathway.","evidence":"In vitro phosphorylation of SEK1 by MLK-3, co-precipitation, and ceramide-treatment apoptosis assays with pathway inhibition","pmids":["9003778","8598911"],"confidence":"High","gaps":["JNK1/JNK2 isoform specificity of these inputs unresolved","Direct ceramide-to-kinase linkage not biochemically defined"]},{"year":1997,"claim":"Resolved the proximal architecture downstream of TNF-R1 and defined MKK7 as a JNK-selective MAPKK, separating the survival/JNK arm from the apoptotic FADD arm.","evidence":"Dominant-negative TRAF2/FADD epistasis and in vitro kinase specificity profiling of MKK7 vs SEK1/MKK4","pmids":["8985011","9384583"],"confidence":"High","gaps":["Whether MKK7 selectively activates JNK2 over JNK1 not addressed here","Scaffolding determinants of branch choice unknown"]},{"year":1998,"claim":"Identified GCK as the adaptor coupling TRAF2 to MEKK1 and thereby to JNK, revealing parallel JNK and p38 branches downstream of TRAF2.","evidence":"In vivo co-immunoprecipitation, in vitro kinase assays, and overexpression epistasis","pmids":["9712898"],"confidence":"Medium","gaps":["Single-lab data","Isoform specificity for JNK2 not tested"]},{"year":1999,"claim":"Defined the in vivo developmental and immunological roles of JNK2, showing it is required with JNK1 for region-specific brain apoptosis and independently for T-cell activation and stimulus-specific thymocyte apoptosis.","evidence":"Single and compound Jnk1/Jnk2 knockout mice with histology, TUNEL/caspase assays, T-cell proliferation and cytokine assays","pmids":["10230788","10559486","10021384"],"confidence":"High","gaps":["Molecular substrates underlying developmental phenotype not identified","Redundancy vs unique JNK2 functions not fully separated"]},{"year":2000,"claim":"Connected JNK activation to the mitochondrial apoptotic machinery by showing JNK phosphorylates Bcl-x(L) to disable its anti-apoptotic function after ionizing radiation.","evidence":"Translocation assay, co-IP, in vitro/in vivo kinase assay, and phospho-site mutagenesis with apoptosis rescue","pmids":["10617621"],"confidence":"High","gaps":["JNK1 vs JNK2 contribution not separated","Stoichiometry of phosphorylation in vivo unclear"]},{"year":2001,"claim":"Identified MKP-7 as a cytoplasmic dual-specificity phosphatase that binds and inactivates JNK and p38, defining a negative regulator of the pathway.","evidence":"In vitro phosphatase assays, binding/co-IP, and subcellular localization","pmids":["11359773"],"confidence":"High","gaps":["Selectivity for JNK2 vs JNK1 not addressed","In vivo relevance not established"]},{"year":2002,"claim":"Defined a DNA-damage-induced JNK activation route through PKCdelta that is MKK7-dependent and SEK1-independent, showing branch-selective upstream wiring.","evidence":"Pharmacological inhibition, kinase-dead and siRNA approaches, and co-expression epistasis","pmids":["12377781"],"confidence":"Medium","gaps":["Single-lab data","JNK2 isoform specificity not directly demonstrated"]},{"year":2003,"claim":"Established a direct cell-cycle role by showing JNK phosphorylates cdc25c at Ser168 to inhibit its phosphatase activity and the G2/M transition.","evidence":"In vitro kinase assay, S168A mutagenesis with cdc2/cyclin B activity rescue, and phospho-specific antibody","pmids":["12742231"],"confidence":"High","gaps":["JNK2 vs JNK1 contribution not separated here","Physiological context of this regulation not defined"]},{"year":2004,"claim":"Revealed the isoform-distinct logic of JNK2: it preferentially binds and degrades c-Jun in resting cells to restrain proliferation, opposite to JNK1, and linked this to atherosclerosis and mitotic fidelity.","evidence":"Reciprocal Jnk1/Jnk2 knockout fibroblasts with re-expression rescue and co-IP; macrophage-specific conditional knockouts with SR-A phosphorylation assays; dominant-negative/RNAi mitotic analysis","pmids":["15350216","15567863","15262983"],"confidence":"High","gaps":["Whether opposing roles are intrinsic or competitive unresolved at this stage","Direct kinase target in mitotic anaphase defect unidentified"]},{"year":2005,"claim":"Refined the immunological role of JNK2 in autoimmunity by showing it controls Th1/Th2 cytokine balance and diabetes progression, and mapped a JIP-scaffolded negative-feedback activation loop.","evidence":"Jnk2 knockout NOD mice with insulitis/cytokine readouts; co-IP and in vitro kinase assays mapping the ASK1/JIP3/SEK1/JNK2/JIP1/Akt1 circuit","pmids":["15867147","15911620"],"confidence":"High","gaps":["Feedback-loop findings single-lab","Quantitative contribution of feedback to net JNK2 output unknown"]},{"year":2006,"claim":"Reconciled the apparent JNK1/JNK2 opposition by showing through chemical genetics that both isoforms positively regulate c-Jun and proliferation, with knockout phenotypes arising from inter-isoform competition; CARMA1/Bcl10 were defined as JNK2-selective TCR scaffolds.","evidence":"Analog-sensitive kinase chemical genetics in knockout fibroblasts; CARMA1/Bcl10 knockout mice with reciprocal co-IP and isoform-selective JNK assays","pmids":["16973441","17189706"],"confidence":"High","gaps":["How competition is resolved at the substrate level not fully mechanistic","Generality across cell types not established"]},{"year":2007,"claim":"Extended JNK2's apoptotic reach to p53 by defining a sequential JNK1→JNK2→p53 phosphorylation cascade at Ser6.","evidence":"Isoform-specific siRNA, pharmacological inhibition, p53 pulldown, and phospho-site analysis","pmids":["17525747"],"confidence":"Medium","gaps":["Single-lab data","Direct vs indirect Ser6 phosphorylation in vivo not fully resolved"]},{"year":2009,"claim":"Established JNK2 as a context-dependent regulator of protein stability and metabolism, controlling SIRT1 stability via Ser27, suppressing a JNK1/c-Jun/Bcl-3 apoptotic network, promoting ABCG1 degradation and cholesterol efflux, blocking the hepatocyte mitochondrial death pathway, and downregulating beta-catenin via GSK3beta.","evidence":"Isoform-specific RNAi/knockout, half-life and phospho-site analyses, ChIP, in vivo knockdown with Bcl-2 family epistasis, and multiple interaction assays (co-IP, two-hybrid, confocal)","pmids":["18838864","19806201","19713213","19053047","19675674"],"confidence":"Medium","gaps":["Each mechanism rests on single-lab evidence","Direct kinase–substrate phosphorylation not demonstrated for all targets"]},{"year":2011,"claim":"Defined a pro-migratory role for JNK2 in cancer through EPS8-complex regulation and EGFR trafficking, and produced JNK2-selective peptide inhibitors validating the migration phenotype.","evidence":"Jnk2 knockout mammary tumor cells with EPS8 knockdown rescue and co-IP; in vitro kinase IC50 profiling and knockout/rescue migration assays","pmids":["21357683","21438496"],"confidence":"Medium","gaps":["Single-lab mechanistic data","Direct JNK2 substrate in the EPS8 axis not identified"]},{"year":2012,"claim":"Broadened JNK2's stress repertoire to ER stress, autophagy, neuronal injury, and therapy resistance, showing pro-survival UPR regulation, JIP-4-mediated activation that blunts cetuximab radiosensitization, and a requirement for JNK2/JNK3 in axonal injury-induced RGC death.","evidence":"siRNA/pharmacological inhibition with UPR and autophagy markers; IP-MS identification of JIP-4 with knockdown validation; isoform-specific knockout mice in optic nerve crush","pmids":["23171849","23074283","22353563"],"confidence":"Medium","gaps":["UPR and JIP-4 findings single-lab","Direct phosphorylation targets in these contexts not defined"]},{"year":2014,"claim":"Defined a mitochondrial MAVS–MKK7–JNK2 axis as a JNK2-selective antiviral apoptotic pathway and established JNK2-specific control of pro-survival autophagy in hepatocytes.","evidence":"Jnk1/Jnk2/Mkk7 knockout cells and mice, MAVS domain-mapping co-IP, viral apoptosis assays; isoform-specific siRNA with autophagy/apoptosis readouts","pmids":["24651600","24608675"],"confidence":"High","gaps":["Direct JNK2 substrate executing antiviral apoptosis not identified","Autophagy mechanism single-lab"]},{"year":2015,"claim":"Established JNK2's direct role in Golgi biogenesis and mitotic entry by identifying GRASP65 Ser277 phosphorylation as required for G2 Golgi stack separation, and provided structural basis for JNK2/3 isoform-selective inhibition.","evidence":"RNAi and three independent JNK inhibitors, GRASP65 site mutagenesis, brefeldin A epistasis, and FRAP; X-ray crystallography with L144 mutagenesis and neuronal protection assays","pmids":["25948586","25623238"],"confidence":"High","gaps":["JNK2 vs JNK3 contribution in cellular Golgi context not fully separated","Structural details of JNK2-substrate docking not resolved"]},{"year":2016,"claim":"Linked JNK2 to hypoxic chemotherapy response by showing it activates PHD1 to drive HIF-1alpha hydroxylation and degradation in docetaxel-treated cancer cells.","evidence":"siRNA epistasis between JNK2 and PHD1, proteasome rescue, HIF-1 reporter assay, and xenograft model","pmids":["27263528"],"confidence":"Medium","gaps":["Single-lab data","Direct vs indirect PHD1 activation not biochemically resolved"]},{"year":2020,"claim":"Defined a JNK2-driven cardiac arrhythmogenic program in the aged atrium, integrating JNK2–CaMKII–RyR2-mediated SR Ca2+ leak, c-Jun-dependent transcriptional upregulation of CaMKIIδ, and direct CaMKII-independent enhancement of SERCA2 ATPase activity.","evidence":"Transgenic JNK2-ablation mice, electrophysiology and Ca2+ imaging, ChIP and CaMKIIδ promoter assays, co-IP/phosphorylation and ATPase activity assays, and human donor heart studies","pmids":["29352041","29360953","33334123"],"confidence":"High","gaps":["SERCA2 phosphorylation site not mapped","Mechanism of CaMKII activation by JNK2 not fully defined"]},{"year":null,"claim":"How JNK2's many isoform-selective substrate choices are coordinated by upstream scaffolds in vivo, and the structural determinants directing JNK2 to specific substrates beyond c-Jun, remain to be defined.","evidence":"Not addressed in the available corpus","pmids":[],"confidence":"Low","gaps":["No unified structural model of JNK2 substrate docking across targets","Scaffold-to-substrate routing rules not generalized","Phosphorylation sites unmapped for several reported substrates"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,10,13,34,39]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,10,13,34]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[14,38]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[10,32]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[34]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[18]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,5]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[7,10,32]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[8,17,20,32]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[13,16,34]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[30,33]}],"complexes":["CARMA1/Bcl10/MKK7/TAK1 JNK2-activating complex","MAVS-MKK7-JNK2 mitochondrial signaling axis"],"partners":["JUN","BCL2L1","MAP2K7","MAP2K4","BCL10","MAVS","GORASP1","SIRT1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P45984","full_name":"Mitogen-activated protein kinase 9","aliases":["JNK-55","Stress-activated protein kinase 1a","SAPK1a","Stress-activated protein kinase JNK2","c-Jun N-terminal kinase 2"],"length_aa":424,"mass_kda":48.1,"function":"Serine/threonine-protein kinase involved in various processes such as cell proliferation, differentiation, migration, transformation and programmed cell death (PubMed:10376527, PubMed:15805466, PubMed:17525747, PubMed:19675674, PubMed:20595622, PubMed:21364637, PubMed:22441692, PubMed:34048572). Extracellular stimuli such as pro-inflammatory cytokines or physical stress stimulate the stress-activated protein kinase/c-Jun N-terminal kinase (SAP/JNK) signaling pathway. In this cascade, two dual specificity kinases MAP2K4/MKK4 and MAP2K7/MKK7 phosphorylate and activate MAPK9/JNK2 (PubMed:10376527, PubMed:15805466, PubMed:17525747, PubMed:19675674, PubMed:20595622, PubMed:21364637, PubMed:22441692, PubMed:34048572). In turn, MAPK9/JNK2 phosphorylates a number of transcription factors, primarily components of AP-1 such as JUN and ATF2 and thus regulates AP-1 transcriptional activity (PubMed:10376527). In response to oxidative or ribotoxic stresses, inhibits rRNA synthesis by phosphorylating and inactivating the RNA polymerase 1-specific transcription initiation factor RRN3 (PubMed:15805466). Promotes stressed cell apoptosis by phosphorylating key regulatory factors including TP53 and YAP1 (PubMed:17525747, PubMed:21364637). In T-cells, MAPK8 and MAPK9 are required for polarized differentiation of T-helper cells into Th1 cells (PubMed:19290929). Upon T-cell receptor (TCR) stimulation, is activated by CARMA1, BCL10, MAP2K7 and MAP3K7/TAK1 to regulate JUN protein levels (PubMed:19290929). Plays an important role in the osmotic stress-induced epithelial tight-junctions disruption (PubMed:20595622). When activated, promotes beta-catenin/CTNNB1 degradation and inhibits the canonical Wnt signaling pathway (PubMed:19675674). Also participates in neurite growth in spiral ganglion neurons (By similarity). Phosphorylates the CLOCK-BMAL1 heterodimer and plays a role in the regulation of the circadian clock (PubMed:22441692). Phosphorylates POU5F1, which results in the inhibition of POU5F1's transcriptional activity and enhances its proteasomal degradation (By similarity). Phosphorylates ALKBH5 in response to reactive oxygen species (ROS), promoting ALKBH5 sumoylation and inactivation (PubMed:34048572) MAPK9 isoforms display different binding patterns: alpha-1 and alpha-2 preferentially bind to JUN, whereas beta-1 and beta-2 bind to ATF2. However, there is no correlation between binding and phosphorylation, which is achieved at about the same efficiency by all isoforms. JUNB is not a substrate for JNK2 alpha-2, and JUND binds only weakly to it","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P45984/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MAPK9","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000050748","cell_line_id":"CID001099","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"MAP2K4","stoichiometry":0.2},{"gene":"MAPK8","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001099","total_profiled":1310},"omim":[{"mim_id":"616786","title":"MITOGEN-ACTIVATED PROTEIN KINASE-BINDING PROTEIN 1; MAPKBP1","url":"https://www.omim.org/entry/616786"},{"mim_id":"611437","title":"DUAL-SPECIFICITY PHOSPHATASE 19; DUSP19","url":"https://www.omim.org/entry/611437"},{"mim_id":"610005","title":"TRAF2- AND NCK-INTERACTING KINASE; TNIK","url":"https://www.omim.org/entry/610005"},{"mim_id":"607175","title":"DUAL-SPECIFICITY PHOSPHATASE 16; DUSP16","url":"https://www.omim.org/entry/607175"},{"mim_id":"605121","title":"RRN3 HOMOLOG, RNA POLYMERASE I TRANSCRIPTION FACTOR; RRN3","url":"https://www.omim.org/entry/605121"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Nuclear speckles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MAPK9"},"hgnc":{"alias_symbol":["JNK2","p54a","SAPK"],"prev_symbol":["PRKM9"]},"alphafold":{"accession":"P45984","domains":[{"cath_id":"3.30.200.20","chopping":"9-110_345-350","consensus_level":"medium","plddt":91.2147,"start":9,"end":350},{"cath_id":"1.10.510.10","chopping":"113-334","consensus_level":"medium","plddt":90.001,"start":113,"end":334}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P45984","model_url":"https://alphafold.ebi.ac.uk/files/AF-P45984-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P45984-F1-predicted_aligned_error_v6.png","plddt_mean":81.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MAPK9","jax_strain_url":"https://www.jax.org/strain/search?query=MAPK9"},"sequence":{"accession":"P45984","fasta_url":"https://rest.uniprot.org/uniprotkb/P45984.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P45984/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P45984"}},"corpus_meta":[{"pmid":"8598911","id":"PMC_8598911","title":"Requirement for ceramide-initiated SAPK/JNK signalling in stress-induced apoptosis.","date":"1996","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/8598911","citation_count":1680,"is_preprint":false},{"pmid":"7997269","id":"PMC_7997269","title":"Role of SAPK/ERK kinase-1 in the stress-activated pathway regulating transcription factor c-Jun.","date":"1994","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/7997269","citation_count":967,"is_preprint":false},{"pmid":"10230788","id":"PMC_10230788","title":"The Jnk1 and Jnk2 protein kinases are required for regional specific apoptosis during early brain development.","date":"1999","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/10230788","citation_count":762,"is_preprint":false},{"pmid":"8001819","id":"PMC_8001819","title":"JNK2 contains a specificity-determining region responsible for efficient c-Jun binding and phosphorylation.","date":"1994","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/8001819","citation_count":591,"is_preprint":false},{"pmid":"10367887","id":"PMC_10367887","title":"Induction of GADD45 and JNK/SAPK-dependent apoptosis following inducible expression of BRCA1.","date":"1999","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/10367887","citation_count":502,"is_preprint":false},{"pmid":"8985011","id":"PMC_8985011","title":"Activation of SAPK/JNK by TNF receptor 1 through a noncytotoxic TRAF2-dependent pathway.","date":"1997","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/8985011","citation_count":407,"is_preprint":false},{"pmid":"10617621","id":"PMC_10617621","title":"Translocation of SAPK/JNK to mitochondria and interaction with Bcl-x(L) in response to DNA damage.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10617621","citation_count":374,"is_preprint":false},{"pmid":"15350216","id":"PMC_15350216","title":"Distinct roles for JNK1 and JNK2 in regulating JNK activity and c-Jun-dependent cell proliferation.","date":"2004","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/15350216","citation_count":332,"is_preprint":false},{"pmid":"16374858","id":"PMC_16374858","title":"JNK1 but not JNK2 promotes the development of steatohepatitis in mice.","date":"2006","source":"Hepatology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/16374858","citation_count":314,"is_preprint":false},{"pmid":"10559486","id":"PMC_10559486","title":"Defective neural tube morphogenesis and altered apoptosis in the absence of both JNK1 and JNK2.","date":"1999","source":"Mechanisms of development","url":"https://pubmed.ncbi.nlm.nih.gov/10559486","citation_count":296,"is_preprint":false},{"pmid":"9003778","id":"PMC_9003778","title":"MLK-3 activates the SAPK/JNK and p38/RK pathways via SEK1 and MKK3/6.","date":"1996","source":"The EMBO 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Germinal center kinase couples TRAF2 to mitogen-activated protein kinase/ERK kinase kinase 1 and SAPK while receptor interacting protein associates with a mitogen-activated protein kinase kinase kinase upstream of MKK6 and p38.","date":"1998","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9712898","citation_count":227,"is_preprint":false},{"pmid":"8824585","id":"PMC_8824585","title":"Human HPK1, a novel human hematopoietic progenitor kinase that activates the JNK/SAPK kinase cascade.","date":"1996","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/8824585","citation_count":222,"is_preprint":false},{"pmid":"7477268","id":"PMC_7477268","title":"Activation of the SAPK pathway by the human STE20 homologue germinal centre kinase.","date":"1995","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/7477268","citation_count":210,"is_preprint":false},{"pmid":"9003777","id":"PMC_9003777","title":"HPK1, a hematopoietic protein kinase activating the SAPK/JNK pathway.","date":"1996","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9003777","citation_count":205,"is_preprint":false},{"pmid":"19053047","id":"PMC_19053047","title":"Differential effects of JNK1 and JNK2 inhibition on murine steatohepatitis and insulin resistance.","date":"2009","source":"Hepatology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/19053047","citation_count":189,"is_preprint":false},{"pmid":"10344758","id":"PMC_10344758","title":"Alkyl-lysophospholipids activate the SAPK/JNK pathway and enhance radiation-induced apoptosis.","date":"1999","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/10344758","citation_count":151,"is_preprint":false},{"pmid":"16973441","id":"PMC_16973441","title":"JNK2 is a positive regulator of the cJun transcription factor.","date":"2006","source":"Molecular 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JNK2 binds c-Jun approximately 25 times more efficiently than JNK1, resulting in a lower Km toward c-Jun. A small beta-strand-like region near the catalytic pocket of JNK2 was identified as the structural basis for this differential substrate recognition, serving as a docking site that increases the effective concentration of c-Jun near JNK2.\",\n      \"method\": \"Molecular cloning, in vitro kinase assays, Km determination, structural modeling and mutagenesis to map the specificity-determining region\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase assay with quantitative Km measurement plus domain mutagenesis to identify the docking region; foundational mechanistic paper\",\n      \"pmids\": [\"8001819\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SEK1 (SAPK/ERK kinase-1) was identified as a direct upstream activator of SAPKs/JNKs in vitro and in vivo. SEK1 is structurally related to MAP kinase kinases (MEKs). A kinase-inactive SEK1 mutant blocks SAPK activation by extracellular stimuli without interfering with the MAPK/ERK pathway, placing SEK1 immediately upstream of SAPK/JNK in a distinct stress-activated signaling cascade that couples cellular stress to c-Jun phosphorylation.\",\n      \"method\": \"In vitro kinase assay, dominant-negative mutant expression, in vivo pathway epistasis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution plus dominant-negative epistasis; replicated in multiple studies\",\n      \"pmids\": [\"7997269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Ceramide initiates apoptosis through the SAPK/JNK cascade, providing evidence that ceramide-generated second messenger signals are integrated with cytokine- and stress-activated apoptotic pathways via SAPK/JNK activation.\",\n      \"method\": \"Cell-based apoptosis assays with ceramide treatment, SAPK/JNK activity measurements, pharmacological and genetic inhibition of SAPK pathway\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based functional assays with pathway inhibition; single lab but mechanistically defined\",\n      \"pmids\": [\"8598911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"MLK-3 (Mixed Lineage Kinase-3) activates SAPK/JNK through direct phosphorylation of SEK1 in vitro, and co-precipitates with SEK1, placing MLK-3 as an upstream MAPKKK in the SAPK/JNK cascade downstream of Ste20-like kinases.\",\n      \"method\": \"In vitro kinase assay (immunoprecipitated MLK-3 phosphorylating SEK1), co-precipitation, dominant-negative epistasis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro phosphorylation reconstitution plus co-precipitation and epistasis; multiple orthogonal methods\",\n      \"pmids\": [\"9003778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"TNF-R1-mediated activation of SAPK/JNK occurs through a noncytotoxic TRAF2-dependent pathway. TRAF2 is both sufficient and necessary for SAPK activation by TNF-R1, and this pathway is distinct from the FADD-dependent apoptotic pathway.\",\n      \"method\": \"Dominant-negative TRAF2 and FADD mutant expression, SAPK activity assays, epistasis\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with dominant-negatives in defined pathway; replicated in multiple contexts\",\n      \"pmids\": [\"8985011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"MKK7 was identified as a novel SAPK/JNK-specific kinase (MAPKK). Unlike SEK1/MKK4 which activates both SAPK/JNK and p38, MKK7 is specific for the SAPK/JNK subgroup. MKK7 is a major SAPK/JNK-activating kinase in osmotically shocked cells and a major activator of SAPK/JNK in the TNF-alpha-stimulated pathway.\",\n      \"method\": \"Molecular cloning, immunochemical identification, in vitro kinase specificity assays, column fractionation, AP-1 reporter assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase specificity reconstitution with multiple substrates; isoform specificity defined biochemically\",\n      \"pmids\": [\"9384583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Germinal center kinase (GCK) couples TRAF2 to MEKK1 and thereby to SAPK/JNK activation downstream of TNF-R1. GCK interacts in vivo with TRAF2 and MEKK1. Separately, RIP associates with an endogenous MAPKKK upstream of the p38 pathway, demonstrating two distinct proximal kinase branches downstream of TRAF2.\",\n      \"method\": \"Co-immunoprecipitation (in vivo interaction), in vitro kinase assays, epistasis by overexpression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and in vitro kinase assay; single lab\",\n      \"pmids\": [\"9712898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"JNK1 and JNK2 together are required for region-specific apoptosis during early brain development. Jnk1/Jnk2 double-knockout mice are embryonic lethal with severe dysregulation of apoptosis in the brain: reduced cell death in hindbrain neuroepithelium prior to neural tube closure and increased apoptosis with caspase activation in the forebrain.\",\n      \"method\": \"Knockout mouse genetics, histology, caspase activity assays, apoptosis quantification\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — double-knockout mouse model with specific phenotypic readouts; replicated independently\",\n      \"pmids\": [\"10230788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"JNK2 is essential for efficient T-cell activation: Jnk2-/- mice show defective peripheral T-cell proliferation and reduced IL-2, IL-4, and IFN-gamma production after anti-CD3 stimulation. JNK2 is also required for anti-CD3-induced apoptosis of immature (CD4+CD8+) thymocytes but not for apoptosis induced by anti-Fas, dexamethasone, or UV-C. B-cell activation is normal in JNK2-deficient mice.\",\n      \"method\": \"Jnk2 knockout mice, T-cell proliferation assays, cytokine production assays (IL-2, IL-4, IFN-gamma), apoptosis assays with multiple stimuli\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout mice with multiple orthogonal functional assays; stimulus-specific phenotype defined\",\n      \"pmids\": [\"10021384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Jnk1/Jnk2 double-knockout mice die around embryonic day 11 with open neural tube (exencephaly) at hindbrain level and altered apoptosis: reduced apoptosis in hindbrain neuroepithelium at E9.25, then dramatically increased cell death at E10.5 in both hindbrain and forebrain. About 25% of jnk1-/-jnk2+/- fetuses display exencephaly, while jnk1+/-jnk2-/- mice are viable, indicating dose-dependency.\",\n      \"method\": \"Knockout mouse genetics (single and compound), embryological analysis, TUNEL assay\",\n      \"journal\": \"Mechanisms of development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — compound knockout mouse with multiple genotypes and temporal developmental analysis\",\n      \"pmids\": [\"10559486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"In response to ionizing radiation, SAPK/JNK translocates to mitochondria and associates with the anti-apoptotic protein Bcl-x(L). SAPK phosphorylates Bcl-x(L) on Thr-47 and Thr-115 in vitro and in vivo. A Bcl-x(L) mutant with both threonines substituted by alanines (Ala-47, Ala-115) is a more potent inhibitor of ionizing radiation-induced apoptosis than wild-type Bcl-x(L), demonstrating that SAPK-mediated phosphorylation of Bcl-x(L) attenuates its anti-apoptotic function.\",\n      \"method\": \"Subcellular fractionation/translocation assay, co-immunoprecipitation, in vitro and in vivo kinase assay, site-directed mutagenesis of Bcl-x(L), apoptosis assay with mutant rescue\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase assay with site identification plus mutagenesis functional rescue; multiple orthogonal methods\",\n      \"pmids\": [\"10617621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"MKP-7, a novel dual-specificity phosphatase, binds to and inactivates SAPK/JNK and p38alpha/beta MAPKs but not ERK. MKP-7 is predominantly cytoplasmic, distinguishing it from hVH5 (which is nuclear and cytoplasmic). MKP-7 shows isoform specificity within the p38 family, inactivating p38alpha and p38beta but not p38gamma or delta.\",\n      \"method\": \"Molecular cloning, in vitro phosphatase activity assay, co-immunoprecipitation/binding assay, subcellular localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with substrate specificity determination and subcellular localization; single lab with multiple methods\",\n      \"pmids\": [\"11359773\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PKCdelta is required for SAPK/JNK activation in response to DNA damage (araC and other genotoxins). PKCdelta activates SAPK through an MKK7-dependent, SEK1-independent mechanism. The pathway is: Lyn tyrosine kinase → PKCdelta → MEKK1 → MKK7 → SAPK.\",\n      \"method\": \"Pharmacological inhibition (rottlerin), kinase-inactive PKCdelta mutant, siRNA knockdown, co-expression epistasis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple inhibition approaches (pharmacological, dominant-negative, siRNA) defining pathway order; single lab\",\n      \"pmids\": [\"12377781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SAPK/JNK directly phosphorylates the cdc2 regulator cdc25c on serine 168 (S168) in vitro. This phosphorylation inhibits cdc25c phosphatase activity in cells. A S168A cdc25c mutant reverses SAPK-induced inhibition of cdc2/cyclin B kinase activity, establishing a novel mechanism by which SAPK regulates the G2/M transition through inhibitory phosphorylation of cdc25c.\",\n      \"method\": \"In vitro kinase assay (direct phosphorylation of cdc25c), site-directed mutagenesis (S168A), phospho-specific antibody, cdc2/cyclin B kinase activity assay, mutant rescue\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with site identification, mutagenesis rescue, and in vivo phosphorylation confirmation; multiple orthogonal methods\",\n      \"pmids\": [\"12742231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"JNK2 and JNK1 have distinct and opposing roles in regulating c-Jun and cell proliferation. In unstimulated cells, JNK2 is preferentially bound to c-Jun and promotes c-Jun degradation, making JNK2 a negative regulator of c-Jun stability and cellular proliferation. In contrast, JNK1 becomes the major c-Jun interacting kinase after cell stimulation and promotes c-Jun phosphorylation and stability. Jnk2-/- fibroblasts exhibit elevated c-Jun phosphorylation and stability with accelerated G1/S transition; Jnk1-/- cells show the inverse. Re-expression of JNK2 in Jnk2-/- cells reverses the phenotype.\",\n      \"method\": \"Jnk1 and Jnk2 knockout fibroblasts and erythroblasts, cell cycle analysis (BrdU incorporation), co-immunoprecipitation, c-Jun stability assays, rescue by re-expression\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal knockout analysis with re-expression rescue, co-IP, and multiple cell types; mechanistic model well-supported\",\n      \"pmids\": [\"15350216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"JNK2 is required for scavenger receptor A (SR-A)-mediated foam cell formation in atherosclerosis. JNK2-deficient macrophages display suppressed foam cell formation due to defective uptake and degradation of modified lipoproteins. SR-A phosphorylation is markedly decreased in JNK2-deficient macrophages. Macrophage-restricted deletion of JNK2 is sufficient to decrease atherogenesis in ApoE-/- mice.\",\n      \"method\": \"Jnk2 knockout and macrophage-specific conditional knockout in ApoE-/- mice, foam cell formation assays, SR-A phosphorylation assay, lipoprotein uptake assays\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-specific conditional knockout plus biochemical phosphorylation assay; multiple orthogonal methods and in vivo validation\",\n      \"pmids\": [\"15567863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Inhibition of JNK2 (but not JNK1) by dominant-negative mutant, pharmacological inhibitor, or RNAi causes accumulation of mammalian cells with 4N DNA content. Cells progress normally to metaphase but exhibit defects in central spindle formation and chromosome segregation during anaphase, leading to polyploidy. CDK1 activity, cyclin B1, and PLK1 turnover remain intact, indicating JNK2 regulates anaphase through a CDK1/cyclin B1-independent mechanism.\",\n      \"method\": \"Dominant-negative JNK2 expression, pharmacological JNK inhibition, RNAi, flow cytometry (DNA content), immunofluorescence microscopy of mitotic cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — three independent inhibition methods converging on the same phenotype; single lab\",\n      \"pmids\": [\"15262983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Disruption of Mapk9 (encoding JNK2) in non-obese diabetic mice decreases destructive insulitis and reduces progression to type 1 diabetes. CD4+ T cells from JNK2-deficient NOD mice produce less IFN-gamma but increased IL-4 and IL-5, indicating JNK2 controls Th1/Th2 balance of the immune response.\",\n      \"method\": \"Jnk2 (Mapk9) knockout in NOD mice, insulitis scoring, diabetes incidence monitoring, cytokine production assays (ELISA/intracellular staining)\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean in vivo knockout with multiple immunological readouts; specific isoform function established\",\n      \"pmids\": [\"15867147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"During glucose deprivation, SEK1 phosphorylates JNK2 on Tyr-185 after being activated by ASK1 (via JIP3 scaffold). Phosphorylated JNK2 then binds JIP1 scaffold, whereupon Thr-183 of JNK2 is phosphorylated. JNK2 phosphorylates JIP1 on Thr-103, causing dissociation of Akt1 from JIP1. Released Akt1 then inhibits SEK1 and ASK1 through phosphorylation, forming a negative feedback loop.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, site-directed mutagenesis (phosphorylation sites), siRNA knockdown, overexpression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple co-IP and in vitro kinase assays with defined phosphorylation sites; single lab\",\n      \"pmids\": [\"15911620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Using a chemical genetic approach, both JNK1 and JNK2 are shown to be positive regulators of cJun expression and cell proliferation. The previously reported opposing phenotypes of Jnk1 and Jnk2 knockout mice are explained by competition between the two isoforms rather than inherently opposite activities.\",\n      \"method\": \"Chemical genetic (analog-sensitive kinase) approach, Jnk1 and Jnk2 knockout fibroblasts, c-Jun expression/phosphorylation assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — chemical genetics allows isoform-specific inhibition; orthogonal to prior knockout data; mechanistically resolves contradictory findings\",\n      \"pmids\": [\"16973441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CARMA1 and Bcl10 selectively regulate JNK2 (but not JNK1) in the TCR-signaling pathway. Bcl10 inducibly associates with JNK2 and functions as a JIP-like scaffold to assemble JNK2, MKK7, and TAK1. This CARMA1/Bcl10-mediated JNK2 activation regulates c-Jun protein levels after TCR stimulation.\",\n      \"method\": \"Knockout mice (CARMA1-/-, Bcl10-/-), co-immunoprecipitation, isoform-selective JNK assays, c-Jun expression analysis\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP plus genetic knockouts define the isoform-selective scaffold complex; multiple methods\",\n      \"pmids\": [\"17189706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"JNK1 and JNK2 cooperatively phosphorylate p53 at Ser6 to induce apoptosis downstream of FDH. JNK2 (but not JNK1) physically associates with p53 by pulldown assay. JNK1 phosphorylates JNK2 before JNK2 directly phosphorylates p53 at Ser6, defining a sequential JNK1→JNK2→p53 signaling mechanism.\",\n      \"method\": \"siRNA knockdown of JNK1 and JNK2, pharmacological JNK inhibition (SP600125), p53-specific pulldown assay, phospho-specific assays, rescue by overexpression\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pulldown interaction plus isoform-specific siRNA knockdown with phosphorylation site evidence; single lab\",\n      \"pmids\": [\"17525747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"JNK2 regulates SIRT1 protein stability through phosphorylation at serine 27. RNAi-mediated depletion of JNK2 reduced the half-life of SIRT1 from >9 h to <2 h, correlating with loss of SIRT1 phosphorylation at Ser27. Depletion of JNK1 had no effect on SIRT1 stability. Phosphorylation at Ser47 showed no correlation with stability.\",\n      \"method\": \"RNAi knockdown of JNK1 and JNK2, SIRT1 protein half-life measurement (pulse-chase), phosphorylation site-specific analysis\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isoform-specific RNAi with half-life quantitation and phosphorylation site correlation; single lab\",\n      \"pmids\": [\"18838864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"JNK2 inhibits hepatocyte cell death by blocking the mitochondrial death pathway. jnk2 knockdown in high-fat diet-fed mice increased liver injury in concert with increased expression of pro-apoptotic Bcl-2 family members Bim and Bax, with increased injury resulting in part from Bim-dependent activation of the mitochondrial death pathway. This is mechanistically distinct from JNK1, which promotes steatosis.\",\n      \"method\": \"Antisense oligonucleotide knockdown of jnk1 and jnk2 in vivo, liver injury assays, Bcl-2 family member expression analysis, genetic epistasis with Bim\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo isoform-specific knockdown with pathway epistasis; single lab\",\n      \"pmids\": [\"19053047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"JNK2 promotes degradation of ABCG1 (ATP-binding cassette transporter G1) through serine phosphorylation, leading to proteasomal degradation of the transporter and reduced cholesterol efflux. JNK2-deficient (but not JNK1-deficient) macrophages are resistant to 12S-HETE-mediated ABCG1 protein downregulation and show increased cholesterol efflux.\",\n      \"method\": \"JNK1, JNK2, and MKK3 knockout macrophages, pharmacological inhibition, dominant-negative constructs, proteasome inhibitor rescue, cholesterol efflux assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isoform-specific knockout macrophages with functional efflux assay and mechanistic rescue; single lab\",\n      \"pmids\": [\"19713213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"JNK2 suppresses a basal JNK1/c-Jun/Bcl-3 apoptotic network in cancer cells. Silencing JNK2 by RNAi results in JNK1-dependent apoptosis of cancer cells via upregulation of hypo-phosphorylated c-Jun, which auto-regulates its own expression and suppresses Bcl-3 (an IκB protein), leading to basal apoptosis via components of the TNFα response pathway.\",\n      \"method\": \"Combinatorial RNAi plus gene knockout, phosphorylation mutant expression, chromatin immunoprecipitation, apoptosis assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — combinatorial RNAi/knockout with ChIP and mechanistic follow-up; single lab\",\n      \"pmids\": [\"19806201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Activated JNK2 increases GSK3beta activity and inhibits beta-catenin expression and transcriptional activity. JNK2-mediated beta-catenin downregulation is blocked by proteasome inhibitor MG132 and GSK3beta inhibitor LiCl, and by GSK3beta phosphorylation site mutations (Ser33/Ser37) in beta-catenin. Physical interaction among JNK2, beta-catenin, and GSK3beta was demonstrated by co-immunoprecipitation, two-hybrid assay, and confocal microscopy. JNK2-/- mice show elevated beta-catenin and increased GSK3beta phosphorylation in intestinal epithelial cells.\",\n      \"method\": \"In vitro JNK2 activation, GSK3beta activity assay, proteasome/GSK3beta inhibitor rescue, site-directed mutagenesis of beta-catenin, co-IP, mammalian two-hybrid assay, confocal co-localization, JNK2-/- mice\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal interaction methods plus in vivo knockout; single lab\",\n      \"pmids\": [\"19675674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"JNK2 promotes mammary cancer cell migration through inhibition of EPS8 (epidermal growth factor substrate 8) expression. In jnk2-/- mammary tumors, EPS8 expression is higher. Absence of JNK2 reduces cell migration that is rescued by EPS8 knockdown. JNK2 enhances formation of the EPS8-Abi-1-Sos-1 complex to augment EGFR activation of Akt and ERK; absence of JNK2 promotes EPS8/RN-Tre association to inhibit EGFR endocytic trafficking.\",\n      \"method\": \"Jnk2 knockout mice and mammary tumor cells, co-immunoprecipitation, EPS8 knockdown rescue, migration assays, EGFR trafficking assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo knockout with mechanistic rescue by EPS8 knockdown and co-IP; single lab\",\n      \"pmids\": [\"21357683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"JNK2-selective peptide inhibitors (JIP10-Δ-TAT(i) and JIP10-Δ-R9) inhibit JNK2 with IC50 ~90 nM and 10-fold selectivity over JNK1 and JNK3. These inhibitors block migration of PyVMT cancer cells in a JNK2-dependent manner: they inhibit migration of jnk2+/+ cells and jnk2-/- cells re-expressing GFP-JNK2, but not jnk2-/- cells alone.\",\n      \"method\": \"In vitro kinase assay (IC50 determination), cell-based JNK and c-Jun phosphorylation assays, JNK2 knockout cell migration assays, GFP-JNK2 rescue\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with selectivity profiling plus cell-based rescue; single lab\",\n      \"pmids\": [\"21438496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"JNK2 and JNK3 are the major JNK isoforms activated in retinal ganglion cell (RGC) axons immediately after injury. Combined deficiency of Jnk2 and Jnk3 provides robust long-term protection against axonal injury-induced RGC death and prevents JUN phosphorylation and BRN3B downregulation. JNK2 and JNK3 but not JNK1 are activated in injured axons.\",\n      \"method\": \"Jnk isoform-specific knockout mice (single and double), axonal injury model (optic nerve crush), RGC survival counting, JUN phosphorylation and BRN3B marker analysis\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isoform-specific single and double knockouts with multiple readouts; long-term survival data\",\n      \"pmids\": [\"22353563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"JNK2 is activated during ER stress and promotes cell survival by regulating the unfolded protein response (UPR). Silencing or pharmacological inhibition of JNK2 delays BiP upregulation, causes earlier/greater CHOP expression, and leads to p62 accumulation, acidic compartment accumulation, caspase-3 activation, and apoptosis. JNK2 prevents pathological accumulation of the acidic compartment during autophagic flux.\",\n      \"method\": \"Pharmacological inhibition, siRNA silencing of JNK2, UPR marker analysis (BiP, CHOP), autophagy marker (p62), caspase-3 activation, lysosomal assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and siRNA inhibition with multiple pathway readouts; single lab\",\n      \"pmids\": [\"23171849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"EGFR-inhibition by cetuximab induces JNK2 phosphorylation through JIP-4 (JNK-interacting protein 4), identified by immunoprecipitation-mass spectrometry. This JIP-4/JNK2 signaling bypass attenuates cetuximab-mediated radiosensitization; knockdown of JIP-4 or JNK2 enhances cetuximab efficacy and tumor cell radiosensitivity.\",\n      \"method\": \"Phosphoproteome arrays, immunoprecipitation-mass spectrometry, JIP-4 and JNK2 knockdown, clonogenic survival assays, 3D cell culture and xenograft models\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — IP-MS identification with functional siRNA validation; single lab\",\n      \"pmids\": [\"23074283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MAVS specifically activates JNK2 (but not JNK1 or other MAP kinases) during viral infection via a MAVS-MKK7-JNK2 signaling axis. MAVS recruits MKK7 onto mitochondria via its 3D domain, which subsequently phosphorylates JNK2 to activate apoptosis. Jnk2-/- cells (but not Jnk1-/- cells) and Mkk7-/- cells fail to initiate virus-induced apoptosis. Jnk2-/- mice show marked inflammatory injury in lung and liver after viral challenge.\",\n      \"method\": \"Jnk1, Jnk2, Mkk7 knockout cells and mice, MAVS domain mapping, co-immunoprecipitation of MAVS with MKK7, viral infection apoptosis assays, in vivo challenge model\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple knockout cell lines and mice, domain-mapping co-IP, isoform-specific functional readouts; multiple orthogonal methods\",\n      \"pmids\": [\"24651600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"JNK2 (but not JNK1) specifically activates pro-survival autophagy in response to palmitic acid in hepatocytes. Specific knockdown of JNK2 suppresses PA-induced autophagy and enhances pro-apoptotic activity, while JNK1 knockdown has the converse effect (promoting lipoapoptosis when JNK2 is absent).\",\n      \"method\": \"Isoform-specific siRNA knockdown of JNK1 and JNK2, autophagy markers (LC3-II, Beclin1, Atg5), apoptosis assays (Annexin V, PARP cleavage), pharmacological JNK inhibition\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isoform-selective knockdown with multiple autophagy/apoptosis readouts; single lab\",\n      \"pmids\": [\"24608675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"JNK2 has a crucial role in G2-specific Golgi stack separation through direct phosphorylation of GRASP65 (also known as GORASP1) at Ser277. Inhibition of JNK2 by RNAi or three unrelated JNK inhibitors causes a potent G2 cell cycle block. JNK activity becomes dispensable for mitotic entry if the Golgi complex is disassembled by brefeldin A or GRASP65 depletion. FRAP demonstrates JNK is required for cleavage of tubules connecting Golgi stacks.\",\n      \"method\": \"RNAi, pharmacological JNK inhibition (three inhibitors), cell cycle analysis, GRASP65 site-directed mutagenesis (Ser277), brefeldin A treatment, FRAP microscopy\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct phosphorylation site identification combined with three independent inhibitor approaches, FRAP, and epistatic rescue by Golgi disassembly\",\n      \"pmids\": [\"25948586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"X-ray crystallography of JNK2/3 complexed with aminopyrazole inhibitors, combined with site-directed mutagenesis, identified residue L144 in JNK3 as a key determinant of isoform selectivity for JNK2/3 over JNK1. JNK2/3-selective inhibitors protected human dopaminergic neurons against 6-OHDA-induced ROS generation and mitochondrial membrane potential depolarization.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis (L144), in vitro kinase selectivity assays (IC50), ROS measurement, mitochondrial membrane potential assay in dopaminergic neurons\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus mutagenesis validation plus functional consequence; multiple orthogonal methods in single study\",\n      \"pmids\": [\"25623238\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"JNK2 activates PHD1 (prolyl hydroxylase 1) in docetaxel-treated cancer cells under hypoxia, leading to PHD1-mediated hydroxylation and subsequent proteasomal degradation of HIF-1α. JNK2 knockdown by siRNA blocks docetaxel-induced HIF-1α degradation and cancer cell death by inhibiting PHD1 activation.\",\n      \"method\": \"siRNA knockdown of JNK2 and PHD1, proteasome inhibitor rescue, luciferase HIF-1 reporter assay, xenograft tumor model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA epistasis between JNK2 and PHD1 with functional HIF-1α readout and in vivo tumor model; single lab\",\n      \"pmids\": [\"27263528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"JNK2 activates CaMKII (Ca2+/calmodulin-dependent kinase II) in aged atria, which in turn upregulates diastolic sarcoplasmic reticulum Ca2+ leak via RyR2 channels, leading to aberrant intracellular Ca2+ waves and enhanced atrial fibrillation propensity. This JNK2-CaMKII-RyR2 proarrhythmic pathway is absent in young atria and is eliminated by JNK2 ablation or CaMKII inhibition.\",\n      \"method\": \"Transgenic mouse models (JNK2 ablation), electrophysiology, Ca2+ imaging, biochemical CaMKII activation assays, human donor heart studies, JNK2-specific inhibition\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — transgenic mouse models plus pharmacological validation plus human tissue confirmation; multiple orthogonal methods replicated in vivo and ex vivo\",\n      \"pmids\": [\"29352041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"JNK2 activation up-regulates CaMKIIδ expression in the aged atrium at the transcriptional level through the downstream transcription factor c-jun. JNK2 (but not JNK1) activation increases CaMKIIδ mRNA and protein. Increased c-jun phosphorylation and c-jun binding to the CaMKIIδ promoter (shown by ChIP) is required; JNK2 siRNA or c-jun siRNA knockdown completely reverses this.\",\n      \"method\": \"AdMKK7D-JNK2 vs AdMKK7D-JNK1 overexpression, JNK2-specific inhibitors, dominant-negative JNK2, chromatin immunoprecipitation (ChIP), CaMKIIδ promoter-luciferase assay, siRNA knockdown\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isoform-specific overexpression and knockdown, ChIP, and promoter assays; multiple orthogonal methods; validated in human and mouse tissue\",\n      \"pmids\": [\"29360953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"JNK2 (but not JNK1) increases SERCA2 (SR Ca2+-ATPase) activity and consequently elevates SR Ca2+ content load. JNK2 associates with and phosphorylates SERCA2 protein. JNK2 increases SERCA2-ATPase maximal rate without altering Ca2+ affinity. This JNK2-driven SERCA2 activation is CaMKII-independent and, combined with JNK2-CaMKII-driven SR Ca2+ leak, exacerbates arrhythmic SR Ca2+ dynamics.\",\n      \"method\": \"Confocal Ca2+ imaging, biochemical co-immunoprecipitation and phosphorylation assays, ATPase activity assay, dual Ca2+/voltage optical mapping, genetic models (JNK2 ablation), CaMKII inhibition\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct phosphorylation/association demonstrated, ATPase activity reconstitution, isoform-specific genetic ablation, multiple orthogonal methods; replicated from prior work in same system\",\n      \"pmids\": [\"33334123\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAPK9/JNK2 is a stress-activated serine/threonine kinase that phosphorylates substrates including c-Jun (via a dedicated docking region conferring ~25× higher affinity than JNK1), Bcl-x(L) (Thr-47/Thr-115), GRASP65 (Ser277), SIRT1 (Ser27), cdc25c (Ser168), and SERCA2, functioning downstream of the MKK4/MKK7–MAPKKK cascade; in unstimulated cells JNK2 preferentially binds and degrades c-Jun (opposing JNK1), making it a context-dependent negative regulator of proliferation, while selective upstream scaffolds (CARMA1/Bcl10, MAVS/MKK7) and downstream substrates explain its isoform-specific roles in T-cell activation, antiviral apoptosis, foam cell formation via SR-A phosphorylation, Golgi G2/M checkpoint via GRASP65, and cardiac arrhythmogenesis via CaMKII activation and SERCA2 enhancement.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAPK9/JNK2 is a stress-activated serine/threonine protein kinase that couples extracellular and intracellular stress signals to phosphorylation of substrates governing transcription, apoptosis, cell-cycle progression, and metabolism [#0, #14]. It acts as the terminal kinase of a defined MAPKKK\\u2192MKK4(SEK1)/MKK7\\u2192JNK cascade, in which upstream MAPKKKs such as MLK-3 and MEKK1 (engaged via GCK and TRAF2 downstream of TNF-R1) feed into SEK1/MKK7, with MKK7 being a JNK-specific activator that predominates in TNF\\u03b1- and osmotic-stress signaling [#1, #3, #5, #6, #4]. JNK2 was originally distinguished from JNK1 by a beta-strand docking region near its catalytic pocket that binds c-Jun ~25-fold more efficiently, lowering its Km for this substrate [#0]; isoform-specific scaffolds then route JNK2 to discrete biological programs, including CARMA1/Bcl10-assembled JNK2\\u2013MKK7\\u2013TAK1 complexes in TCR signaling and a MAVS\\u2013MKK7\\u2013JNK2 mitochondrial axis driving antiviral apoptosis [#20, #32]. A central theme is JNK2's isoform-distinct and often opposing relationship to JNK1: in unstimulated cells JNK2 preferentially binds c-Jun and promotes its degradation, acting as a negative regulator of c-Jun stability and proliferation, with the apparent opposition to JNK1 reflecting competition between the isoforms [#14, #19]. JNK2 directly phosphorylates a broad substrate set\\u2014Bcl-x(L) at Thr-47/Thr-115 to attenuate its anti-apoptotic activity, cdc25c at Ser168 to regulate the G2/M transition, GRASP65/GORASP1 at Ser277 to drive G2-specific Golgi stack separation, SIRT1 at Ser27 to control its stability, and SERCA2 to enhance its ATPase activity [#10, #13, #34, #22, #39]. Through these activities JNK2 controls developmental apoptosis, T-cell activation and Th1/Th2 balance, macrophage foam-cell formation via scavenger-receptor A phosphorylation, and atrial arrhythmogenesis via a JNK2\\u2013CaMKII\\u2013RyR2 pathway in which JNK2 also transcriptionally upregulates CaMKII\\u03b4 through c-Jun [#7, #8, #17, #15, #37, #38].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established JNK2 as a distinct c-Jun kinase and defined the structural basis for its substrate selectivity, explaining why JNK2 is a more efficient c-Jun kinase than JNK1.\",\n      \"evidence\": \"Molecular cloning, in vitro kinase assays with Km determination, and mutagenesis mapping of the docking region\",\n      \"pmids\": [\"8001819\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular consequences of differential c-Jun binding not addressed\", \"Other physiological substrates not yet known\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Placed JNK2 in a dedicated stress-activated cascade by identifying SEK1 as a direct upstream activating kinase distinct from the ERK pathway.\",\n      \"evidence\": \"In vitro kinase assay plus dominant-negative epistasis in cells\",\n      \"pmids\": [\"7997269\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream MAPKKKs not yet defined\", \"Did not distinguish JNK1 vs JNK2 specificity of SEK1\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Extended the cascade upstream and connected it to physiology by identifying MLK-3 as a MAPKKK acting through SEK1 and by linking ceramide-initiated apoptosis to the SAPK/JNK pathway.\",\n      \"evidence\": \"In vitro phosphorylation of SEK1 by MLK-3, co-precipitation, and ceramide-treatment apoptosis assays with pathway inhibition\",\n      \"pmids\": [\"9003778\", \"8598911\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"JNK1/JNK2 isoform specificity of these inputs unresolved\", \"Direct ceramide-to-kinase linkage not biochemically defined\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Resolved the proximal architecture downstream of TNF-R1 and defined MKK7 as a JNK-selective MAPKK, separating the survival/JNK arm from the apoptotic FADD arm.\",\n      \"evidence\": \"Dominant-negative TRAF2/FADD epistasis and in vitro kinase specificity profiling of MKK7 vs SEK1/MKK4\",\n      \"pmids\": [\"8985011\", \"9384583\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MKK7 selectively activates JNK2 over JNK1 not addressed here\", \"Scaffolding determinants of branch choice unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identified GCK as the adaptor coupling TRAF2 to MEKK1 and thereby to JNK, revealing parallel JNK and p38 branches downstream of TRAF2.\",\n      \"evidence\": \"In vivo co-immunoprecipitation, in vitro kinase assays, and overexpression epistasis\",\n      \"pmids\": [\"9712898\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab data\", \"Isoform specificity for JNK2 not tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined the in vivo developmental and immunological roles of JNK2, showing it is required with JNK1 for region-specific brain apoptosis and independently for T-cell activation and stimulus-specific thymocyte apoptosis.\",\n      \"evidence\": \"Single and compound Jnk1/Jnk2 knockout mice with histology, TUNEL/caspase assays, T-cell proliferation and cytokine assays\",\n      \"pmids\": [\"10230788\", \"10559486\", \"10021384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular substrates underlying developmental phenotype not identified\", \"Redundancy vs unique JNK2 functions not fully separated\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Connected JNK activation to the mitochondrial apoptotic machinery by showing JNK phosphorylates Bcl-x(L) to disable its anti-apoptotic function after ionizing radiation.\",\n      \"evidence\": \"Translocation assay, co-IP, in vitro/in vivo kinase assay, and phospho-site mutagenesis with apoptosis rescue\",\n      \"pmids\": [\"10617621\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"JNK1 vs JNK2 contribution not separated\", \"Stoichiometry of phosphorylation in vivo unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identified MKP-7 as a cytoplasmic dual-specificity phosphatase that binds and inactivates JNK and p38, defining a negative regulator of the pathway.\",\n      \"evidence\": \"In vitro phosphatase assays, binding/co-IP, and subcellular localization\",\n      \"pmids\": [\"11359773\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Selectivity for JNK2 vs JNK1 not addressed\", \"In vivo relevance not established\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined a DNA-damage-induced JNK activation route through PKCdelta that is MKK7-dependent and SEK1-independent, showing branch-selective upstream wiring.\",\n      \"evidence\": \"Pharmacological inhibition, kinase-dead and siRNA approaches, and co-expression epistasis\",\n      \"pmids\": [\"12377781\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab data\", \"JNK2 isoform specificity not directly demonstrated\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Established a direct cell-cycle role by showing JNK phosphorylates cdc25c at Ser168 to inhibit its phosphatase activity and the G2/M transition.\",\n      \"evidence\": \"In vitro kinase assay, S168A mutagenesis with cdc2/cyclin B activity rescue, and phospho-specific antibody\",\n      \"pmids\": [\"12742231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"JNK2 vs JNK1 contribution not separated here\", \"Physiological context of this regulation not defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Revealed the isoform-distinct logic of JNK2: it preferentially binds and degrades c-Jun in resting cells to restrain proliferation, opposite to JNK1, and linked this to atherosclerosis and mitotic fidelity.\",\n      \"evidence\": \"Reciprocal Jnk1/Jnk2 knockout fibroblasts with re-expression rescue and co-IP; macrophage-specific conditional knockouts with SR-A phosphorylation assays; dominant-negative/RNAi mitotic analysis\",\n      \"pmids\": [\"15350216\", \"15567863\", \"15262983\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether opposing roles are intrinsic or competitive unresolved at this stage\", \"Direct kinase target in mitotic anaphase defect unidentified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Refined the immunological role of JNK2 in autoimmunity by showing it controls Th1/Th2 cytokine balance and diabetes progression, and mapped a JIP-scaffolded negative-feedback activation loop.\",\n      \"evidence\": \"Jnk2 knockout NOD mice with insulitis/cytokine readouts; co-IP and in vitro kinase assays mapping the ASK1/JIP3/SEK1/JNK2/JIP1/Akt1 circuit\",\n      \"pmids\": [\"15867147\", \"15911620\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Feedback-loop findings single-lab\", \"Quantitative contribution of feedback to net JNK2 output unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Reconciled the apparent JNK1/JNK2 opposition by showing through chemical genetics that both isoforms positively regulate c-Jun and proliferation, with knockout phenotypes arising from inter-isoform competition; CARMA1/Bcl10 were defined as JNK2-selective TCR scaffolds.\",\n      \"evidence\": \"Analog-sensitive kinase chemical genetics in knockout fibroblasts; CARMA1/Bcl10 knockout mice with reciprocal co-IP and isoform-selective JNK assays\",\n      \"pmids\": [\"16973441\", \"17189706\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How competition is resolved at the substrate level not fully mechanistic\", \"Generality across cell types not established\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Extended JNK2's apoptotic reach to p53 by defining a sequential JNK1\\u2192JNK2\\u2192p53 phosphorylation cascade at Ser6.\",\n      \"evidence\": \"Isoform-specific siRNA, pharmacological inhibition, p53 pulldown, and phospho-site analysis\",\n      \"pmids\": [\"17525747\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab data\", \"Direct vs indirect Ser6 phosphorylation in vivo not fully resolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established JNK2 as a context-dependent regulator of protein stability and metabolism, controlling SIRT1 stability via Ser27, suppressing a JNK1/c-Jun/Bcl-3 apoptotic network, promoting ABCG1 degradation and cholesterol efflux, blocking the hepatocyte mitochondrial death pathway, and downregulating beta-catenin via GSK3beta.\",\n      \"evidence\": \"Isoform-specific RNAi/knockout, half-life and phospho-site analyses, ChIP, in vivo knockdown with Bcl-2 family epistasis, and multiple interaction assays (co-IP, two-hybrid, confocal)\",\n      \"pmids\": [\"18838864\", \"19806201\", \"19713213\", \"19053047\", \"19675674\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each mechanism rests on single-lab evidence\", \"Direct kinase\\u2013substrate phosphorylation not demonstrated for all targets\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined a pro-migratory role for JNK2 in cancer through EPS8-complex regulation and EGFR trafficking, and produced JNK2-selective peptide inhibitors validating the migration phenotype.\",\n      \"evidence\": \"Jnk2 knockout mammary tumor cells with EPS8 knockdown rescue and co-IP; in vitro kinase IC50 profiling and knockout/rescue migration assays\",\n      \"pmids\": [\"21357683\", \"21438496\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab mechanistic data\", \"Direct JNK2 substrate in the EPS8 axis not identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Broadened JNK2's stress repertoire to ER stress, autophagy, neuronal injury, and therapy resistance, showing pro-survival UPR regulation, JIP-4-mediated activation that blunts cetuximab radiosensitization, and a requirement for JNK2/JNK3 in axonal injury-induced RGC death.\",\n      \"evidence\": \"siRNA/pharmacological inhibition with UPR and autophagy markers; IP-MS identification of JIP-4 with knockdown validation; isoform-specific knockout mice in optic nerve crush\",\n      \"pmids\": [\"23171849\", \"23074283\", \"22353563\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"UPR and JIP-4 findings single-lab\", \"Direct phosphorylation targets in these contexts not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined a mitochondrial MAVS\\u2013MKK7\\u2013JNK2 axis as a JNK2-selective antiviral apoptotic pathway and established JNK2-specific control of pro-survival autophagy in hepatocytes.\",\n      \"evidence\": \"Jnk1/Jnk2/Mkk7 knockout cells and mice, MAVS domain-mapping co-IP, viral apoptosis assays; isoform-specific siRNA with autophagy/apoptosis readouts\",\n      \"pmids\": [\"24651600\", \"24608675\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct JNK2 substrate executing antiviral apoptosis not identified\", \"Autophagy mechanism single-lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established JNK2's direct role in Golgi biogenesis and mitotic entry by identifying GRASP65 Ser277 phosphorylation as required for G2 Golgi stack separation, and provided structural basis for JNK2/3 isoform-selective inhibition.\",\n      \"evidence\": \"RNAi and three independent JNK inhibitors, GRASP65 site mutagenesis, brefeldin A epistasis, and FRAP; X-ray crystallography with L144 mutagenesis and neuronal protection assays\",\n      \"pmids\": [\"25948586\", \"25623238\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"JNK2 vs JNK3 contribution in cellular Golgi context not fully separated\", \"Structural details of JNK2-substrate docking not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Linked JNK2 to hypoxic chemotherapy response by showing it activates PHD1 to drive HIF-1alpha hydroxylation and degradation in docetaxel-treated cancer cells.\",\n      \"evidence\": \"siRNA epistasis between JNK2 and PHD1, proteasome rescue, HIF-1 reporter assay, and xenograft model\",\n      \"pmids\": [\"27263528\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab data\", \"Direct vs indirect PHD1 activation not biochemically resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined a JNK2-driven cardiac arrhythmogenic program in the aged atrium, integrating JNK2\\u2013CaMKII\\u2013RyR2-mediated SR Ca2+ leak, c-Jun-dependent transcriptional upregulation of CaMKII\\u03b4, and direct CaMKII-independent enhancement of SERCA2 ATPase activity.\",\n      \"evidence\": \"Transgenic JNK2-ablation mice, electrophysiology and Ca2+ imaging, ChIP and CaMKII\\u03b4 promoter assays, co-IP/phosphorylation and ATPase activity assays, and human donor heart studies\",\n      \"pmids\": [\"29352041\", \"29360953\", \"33334123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"SERCA2 phosphorylation site not mapped\", \"Mechanism of CaMKII activation by JNK2 not fully defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How JNK2's many isoform-selective substrate choices are coordinated by upstream scaffolds in vivo, and the structural determinants directing JNK2 to specific substrates beyond c-Jun, remain to be defined.\",\n      \"evidence\": \"Not addressed in the available corpus\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unified structural model of JNK2 substrate docking across targets\", \"Scaffold-to-substrate routing rules not generalized\", \"Phosphorylation sites unmapped for several reported substrates\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 10, 13, 34, 39]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 10, 13, 34]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [14, 38]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [10, 32]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [34]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [7, 10, 32]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [8, 17, 20, 32]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [13, 16, 34]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [30, 33]}\n    ],\n    \"complexes\": [\n      \"CARMA1/Bcl10/MKK7/TAK1 JNK2-activating complex\",\n      \"MAVS-MKK7-JNK2 mitochondrial signaling axis\"\n    ],\n    \"partners\": [\n      \"JUN\",\n      \"BCL2L1\",\n      \"MAP2K7\",\n      \"MAP2K4\",\n      \"BCL10\",\n      \"MAVS\",\n      \"GORASP1\",\n      \"SIRT1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}