{"gene":"GRIK4","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2000,"finding":"KA1/GluK4 subunit immunoreactivity was localized by immunohistochemistry and electron microscopy to dendritic structures in the CA3 area of the hippocampus (postsynaptic to commissural-associational fibers rather than mossy fiber terminals), CA1 pyramidal cell apical dendrites, cortical layer V pyramidal neurons, GABAergic interneurons, Purkinje cells, and glial cells (oligodendrocytes and astrocytes), indicating a broader CNS distribution than previously appreciated.","method":"Immunohistochemistry with anti-peptide antibody to C-terminus of KA1, electron microscopy, cell fractionation","journal":"Brain research. Molecular brain research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by EM and immunohistochemistry with novel validated antibody, single lab, two orthogonal methods","pmids":["11000488"],"is_preprint":false},{"year":2000,"finding":"The KA1 (GluK4) gene promoter drives expression broadly throughout the developing brain during early postnatal development, becoming restricted mainly to hippocampal CA3 pyramidal cells and dentate gyrus granule cells in the adult brain, as established by YAC transgenic Cre-reporter mice.","method":"YAC transgenic mice expressing Cre from KA1 gene locus, Cre immunohistochemistry, X-gal staining in double transgenic KA1-Cre/lacZ reporter mice","journal":"Brain research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct in vivo reporter system with two orthogonal readouts, single lab","pmids":["10973593"],"is_preprint":false},{"year":2008,"finding":"Proteolytic fragments of laminin, generated via tPA-dependent plasmin activity, up-regulate the KA1 subunit of the kainate receptor in hippocampus following kainate injection. This KA1 up-regulation is required for excitotoxic neurodegeneration: laminin gamma1 KO and tPA KO mice both lack KA1 up-regulation and are resistant to kainate-induced neuronal death. Infusion of plasmin-digested laminin-1 restores KA1 up-regulation and neurodegeneration. Anti-KA1 antibody protects against kainate-induced neuronal death both in vitro and in vivo.","method":"Conditional hippocampal laminin gamma1 KO mice, tPA KO mice, intrahippocampal laminin fragment infusion, anti-KA1 antibody neutralization, in vitro and in vivo neurodegeneration assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple KO models, rescue experiment, antibody neutralization, in vitro and in vivo convergent results in single study","pmids":["19114596"],"is_preprint":false},{"year":2011,"finding":"Genetic ablation of GluK4 (Grik4 knockout mice) produces anxiolytic and antidepressant-like phenotypes (elevated zero maze, marble burying, novelty-induced suppression of feeding, forced swim test, sucrose preference). GluK4 expression is restricted to CA3 hippocampus and dentate gyrus in forebrain. Grik4 KO impairs mossy fiber long-term potentiation, likely through loss of kainate receptor modulation of presynaptic mossy fiber axon excitability.","method":"Grik4 knockout mice, behavioral assays (elevated zero maze, marble burying, novelty-induced suppression of feeding, forced swim test, sucrose preference test), mossy fiber LTP electrophysiology","journal":"Behavioural brain research","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with multiple behavioral readouts and synaptic electrophysiology, multiple orthogonal methods","pmids":["22203159"],"is_preprint":false},{"year":2013,"finding":"GluK4 knockout mice show impaired spatial memory acquisition and recall in Morris water maze, marked hyperactivity, and impaired pre-pulse inhibition. GluK4 KO mice are robustly neuroprotected in CA3 following intrahippocampal kainate injection and throughout the hippocampus following hypoxia-ischemia. Biochemical analysis suggests GluK4 mediates excitotoxicity through the JNK signaling pathway.","method":"GluK4 knockout mice, Morris water maze, pre-pulse inhibition, intrahippocampal kainate injection, hypoxia-ischemia model, Western blot analysis of JNK pathway","journal":"Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with multiple orthogonal behavioral and neurodegeneration readouts plus biochemical pathway analysis","pmids":["23357115"],"is_preprint":false},{"year":2015,"finding":"Forebrain overexpression of grik4 in mice causes social impairment, enhanced anxiety, and depressive states, accompanied by more efficient synaptic information transfer through the hippocampal trisynaptic circuit, demonstrating that increased GluK4 dosage alters synaptic transmission and produces autism spectrum disorder-related behavioral features.","method":"Grik4 forebrain-overexpressing transgenic mice, behavioral assays, hippocampal slice electrophysiology of trisynaptic circuit","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain-of-function transgenic model with multiple behavioral readouts and direct electrophysiological measurement of synaptic transmission","pmids":["26446216"],"is_preprint":false},{"year":2016,"finding":"The X-ray crystal structure of the GluK4 ligand-binding domain (LBD) bound to kainate was solved at 2.05 Å resolution. Binding-site residues in GluK4 are most similar to AMPA receptor subfamily, but domain closure and D1-D2 interlobe contacts induced by kainate are similar to low-affinity kainate receptor GluK1, providing a structural explanation for the high kainate binding affinity of GluK4-LBD.","method":"X-ray crystallography at 2.05 Å, thermofluor assay, radiolabel binding affinity assays","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structure validated by binding affinity data, multiple orthogonal methods","pmids":["27524200"],"is_preprint":false},{"year":2018,"finding":"Mild gain of Grik4 dosage in mouse forebrain enhances synaptic transmission and causes a persistent imbalance of inhibitory and excitatory activity, disturbing circuits responsible for main amygdala outputs. These changes in glutamatergic activity are reversible when Grik4 levels are normalized.","method":"Grik4 forebrain-overexpressing transgenic mice, in vivo electrophysiology, circuit analysis of amygdala outputs, normalization of Grik4 expression","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain-of-function model with electrophysiological circuit analysis and rescue by normalization of gene dosage","pmids":["29949767"],"is_preprint":false},{"year":2008,"finding":"A deletion variant in the 3' UTR of GRIK4 is associated with protection against bipolar disorder. Expression studies showed that deletion-carrying mRNA transcripts were relatively more abundant, suggesting the protective effect is mediated through increased kainate receptor expression, possibly due to differences in RNA secondary structure between insertion and deletion alleles.","method":"Case-control genetic study with replication, mRNA expression analysis of variant carriers","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Low","confidence_rationale":"Tier 3 / Weak — expression difference shown in carriers but mechanism (RNA secondary structure effect) is postulated not directly demonstrated; single lab","pmids":["18824690"],"is_preprint":false},{"year":2010,"finding":"KA1 subunit mRNA and protein are expressed in the substantia gelatinosa of the trigeminal subnucleus caudalis, with expression levels significantly higher in juvenile than adult mice, suggesting an age-dependent role in nociceptive processing.","method":"RT-PCR, Western blot, immunohistochemistry in juvenile, prepubescent, and adult mice","journal":"Journal of veterinary science","confidence":"Low","confidence_rationale":"Tier 3 / Weak — descriptive localization and quantitative expression without functional manipulation, single lab","pmids":["21113098"],"is_preprint":false},{"year":2015,"finding":"Up-regulation of KA1 receptor following intrahippocampal kainate or tunicamycin (ER stress inducer) injection correlates with neuronal death and elevated ER stress marker P-eIF2α, suggesting KA1 participates in transmitting apoptotic signals leading to ER dysfunction and neurodegeneration.","method":"Intrahippocampal microinjection of kainate or tunicamycin in mice, FJB staining for cell death, immunofluorescence for KA1 and P-eIF2α","journal":"Nan fang yi ke da xue xue bao","confidence":"Low","confidence_rationale":"Tier 3 / Weak — correlative immunofluorescence without direct manipulation of KA1; single lab, single method","pmids":["25736111"],"is_preprint":false},{"year":2012,"finding":"KA1 and KA2 kainate receptor subunits are present on the dendritic arbors of direction-selective retinal ganglion cells (DS-RGCs) in both developing and adult mouse retina, but no asymmetric distribution was found that would predict direction selectivity.","method":"Immunocytochemistry, Lucifer yellow injection for DS-RGC morphology, confocal microscopy","journal":"Acta histochemica et cytochemica","confidence":"Low","confidence_rationale":"Tier 3 / Weak — localization study only, negative result for asymmetry, no functional manipulation","pmids":["22489103"],"is_preprint":false}],"current_model":"GluK4 (GRIK4) is a high-affinity kainate-type ionotropic glutamate receptor subunit whose ligand-binding domain crystal structure shows AMPA-like binding-site residues with GluK1-like domain closure explaining high kainate affinity; it is expressed predominantly in hippocampal CA3 and dentate gyrus in adult brain, where it regulates mossy fiber LTP and modulates presynaptic excitability, and its loss (KO mice) produces anxiolytic, antidepressant-like, and neuroprotective phenotypes while its gain (forebrain overexpression) enhances excitatory/inhibitory balance, disrupts amygdala circuit output, and produces autism/schizophrenia-related behaviors; additionally, tPA-dependent laminin proteolysis up-regulates KA1 subunit levels in hippocampus to drive excitotoxic neurodegeneration, an effect blocked by anti-KA1 antibody."},"narrative":{"mechanistic_narrative":"GRIK4 encodes GluK4 (KA1), a high-affinity kainate-type ionotropic glutamate receptor subunit that shapes excitatory transmission in the hippocampal trisynaptic circuit and sets the threshold for glutamate-driven excitotoxicity [PMID:22203159, PMID:23357115]. Structurally, its ligand-binding domain combines AMPA-receptor-like binding-site residues with GluK1-like domain closure and D1-D2 interlobe contacts, accounting for its high kainate affinity [PMID:27524200]. In the adult forebrain GluK4 expression is restricted largely to CA3 pyramidal cells and dentate gyrus granule cells, where the subunit modulates presynaptic mossy fiber excitability and is required for mossy fiber long-term potentiation [PMID:10973593, PMID:22203159]. GluK4 dosage bidirectionally controls circuit function: loss of the gene produces anxiolytic, antidepressant-like, and neuroprotective phenotypes along with impaired spatial memory and pre-pulse inhibition [PMID:22203159, PMID:23357115], whereas forebrain overexpression enhances synaptic information transfer through the trisynaptic circuit, produces a reversible excitatory/inhibitory imbalance that disrupts amygdala output, and generates autism- and depression-related behaviors [PMID:26446216, PMID:29949767]. GluK4 also transduces injury signals: its protein levels are up-regulated in hippocampus through tPA/plasmin-dependent proteolysis of laminin, an event required for kainate-induced excitotoxic neurodegeneration and blocked by anti-KA1 antibody, with downstream signaling through the JNK pathway [PMID:19114596, PMID:23357115].","teleology":[{"year":2000,"claim":"Establishing where the KA1/GluK4 subunit resides was the first step toward assigning it a circuit role; immunolocalization showed a broader CNS distribution than expected and a postsynaptic position in CA3.","evidence":"Anti-peptide antibody immunohistochemistry and electron microscopy across hippocampus, cortex, cerebellum and glia","pmids":["11000488"],"confidence":"Medium","gaps":["Localization alone does not establish a functional or synaptic role","Subunit composition of native receptors at these sites not defined"]},{"year":2000,"claim":"Defining the developmental expression program clarified that GluK4 becomes restricted to the CA3/dentate region in the adult, focusing later functional studies on the trisynaptic circuit.","evidence":"YAC transgenic Cre-reporter mice with Cre immunohistochemistry and X-gal staining","pmids":["10973593"],"confidence":"Medium","gaps":["Reporter expression may not capture all sites of endogenous protein","Functional consequence of restriction not addressed"]},{"year":2008,"claim":"Connecting GluK4 to injury signaling, this work showed that tPA/plasmin-generated laminin fragments up-regulate KA1 and that this up-regulation is causally required for excitotoxic neurodegeneration.","evidence":"Conditional laminin gamma1 KO and tPA KO mice, laminin fragment infusion rescue, and anti-KA1 antibody neutralization in vitro and in vivo","pmids":["19114596"],"confidence":"High","gaps":["Molecular mechanism linking laminin fragments to KA1 transcription/translation not defined","Downstream death pathway not resolved here"]},{"year":2008,"claim":"A human genetic association linked GRIK4 expression level to bipolar disorder risk, raising the possibility that receptor dosage influences mood.","evidence":"Case-control genetic study with replication plus mRNA expression analysis of 3' UTR deletion carriers","pmids":["18824690"],"confidence":"Low","gaps":["RNA secondary structure mechanism is postulated, not demonstrated","No causal link between the variant and circuit phenotype shown"]},{"year":2011,"claim":"Loss-of-function genetics tested GluK4's behavioral and synaptic role, showing it is needed for mossy fiber LTP and that its absence is anxiolytic and antidepressant-like.","evidence":"Grik4 knockout mice with a battery of behavioral assays and mossy fiber LTP electrophysiology","pmids":["22203159"],"confidence":"High","gaps":["Mechanism of presynaptic excitability modulation inferred, not directly measured","Cell-type-specific contributions not separated"]},{"year":2013,"claim":"Extending the KO phenotype, this work tied GluK4 to spatial memory, sensorimotor gating, and—critically—excitotoxic vulnerability via the JNK pathway.","evidence":"Grik4 KO mice in Morris water maze, pre-pulse inhibition, intrahippocampal kainate and hypoxia-ischemia models, with Western analysis of JNK signaling","pmids":["23357115"],"confidence":"High","gaps":["Direct biochemical coupling of GluK4 to JNK not demonstrated","Whether neuroprotection is cell-autonomous unresolved"]},{"year":2015,"claim":"Gain-of-function genetics established that increased GluK4 dosage is itself pathogenic, enhancing trisynaptic transmission and producing autism- and mood-related behaviors.","evidence":"Grik4 forebrain-overexpressing transgenic mice with behavioral assays and hippocampal slice electrophysiology","pmids":["26446216"],"confidence":"High","gaps":["Molecular basis of enhanced transmission not dissected","Relationship to human dosage variation not established"]},{"year":2016,"claim":"The crystal structure answered why GluK4 binds kainate with high affinity, revealing AMPA-like binding residues paired with GluK1-like domain closure.","evidence":"X-ray crystallography of the GluK4 LBD bound to kainate at 2.05 Å with thermofluor and radioligand binding","pmids":["27524200"],"confidence":"High","gaps":["Full-length receptor and gating not addressed","Heteromeric assembly behavior not structurally defined"]},{"year":2018,"claim":"Refining the dosage model, mild Grik4 overexpression was shown to cause a reversible excitatory/inhibitory imbalance disrupting amygdala output, demonstrating circuit-level reversibility.","evidence":"Grik4 forebrain-overexpressing transgenic mice with in vivo electrophysiology, amygdala circuit analysis, and normalization of gene dosage","pmids":["29949767"],"confidence":"High","gaps":["Synaptic locus of the imbalance not pinpointed","Translation to therapeutic dosage modulation untested"]},{"year":null,"claim":"How GluK4 dosage and laminin/tPA-driven up-regulation are coupled mechanistically to JNK- and ER-stress-dependent death versus circuit-level behavioral outcomes remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No direct molecular link between GluK4 and JNK or ER-stress effectors established","Subunit composition of native GluK4-containing receptors in each circuit undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[3,6]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[6]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,11]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[3,5]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[2,4]}],"complexes":["kainate receptor"],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q16099","full_name":"Glutamate receptor ionotropic, kainate 4","aliases":["Excitatory amino acid receptor 1","EAA1","Glutamate receptor KA-1","KA1"],"length_aa":956,"mass_kda":107.2,"function":"Ionotropic glutamate receptor that functions as a cation-permeable ligand-gated ion channel. Cannot form functional channels on its own (PubMed:8263508). Shows channel activity only in heteromeric assembly with GRIK1, GRIK2 and GRIK3 subunits (By similarity)","subcellular_location":"Cell membrane; Postsynaptic cell membrane; Presynaptic cell membrane","url":"https://www.uniprot.org/uniprotkb/Q16099/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GRIK4","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GRIK4","total_profiled":1310},"omim":[{"mim_id":"609670","title":"MIGRAINE WITH AURA, SUSCEPTIBILITY TO, 9","url":"https://www.omim.org/entry/609670"},{"mim_id":"600283","title":"GLUTAMATE RECEPTOR, IONOTROPIC, KAINATE 5; GRIK5","url":"https://www.omim.org/entry/600283"},{"mim_id":"600282","title":"GLUTAMATE RECEPTOR, IONOTROPIC, KAINATE 4; GRIK4","url":"https://www.omim.org/entry/600282"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":6.3}],"url":"https://www.proteinatlas.org/search/GRIK4"},"hgnc":{"alias_symbol":["GluK4","KA1"],"prev_symbol":["GRIK"]},"alphafold":{"accession":"Q16099","domains":[{"cath_id":"3.40.50.2300","chopping":"25-137_303-351","consensus_level":"high","plddt":84.616,"start":25,"end":351},{"cath_id":"3.40.50.2300","chopping":"144-270_375-410","consensus_level":"high","plddt":82.2398,"start":144,"end":410},{"cath_id":"3.40.190.10","chopping":"413-517_757-775","consensus_level":"high","plddt":90.3731,"start":413,"end":775},{"cath_id":"3.40.190.10","chopping":"527-532_650-741","consensus_level":"high","plddt":89.3329,"start":527,"end":741},{"cath_id":"1.10.287.70","chopping":"546-576_589-646","consensus_level":"high","plddt":87.8113,"start":546,"end":646}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16099","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q16099-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q16099-F1-predicted_aligned_error_v6.png","plddt_mean":78.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GRIK4","jax_strain_url":"https://www.jax.org/strain/search?query=GRIK4"},"sequence":{"accession":"Q16099","fasta_url":"https://rest.uniprot.org/uniprotkb/Q16099.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q16099/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16099"}},"corpus_meta":[{"pmid":"17671280","id":"PMC_17671280","title":"Association of GRIK4 with outcome of antidepressant treatment in the STAR*D cohort.","date":"2007","source":"The American journal of psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/17671280","citation_count":156,"is_preprint":false},{"pmid":"9832144","id":"PMC_9832144","title":"Expression of NMDAR1, GluR1, GluR7, and KA1 glutamate receptor mRNAs is decreased in frontal cortex of \"neuroleptic-free\" schizophrenics: evidence on reversible up-regulation by typical neuroleptics.","date":"1998","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9832144","citation_count":145,"is_preprint":false},{"pmid":"16819533","id":"PMC_16819533","title":"Cytogenetic and genetic evidence supports a role for the kainate-type glutamate receptor gene, GRIK4, in schizophrenia and bipolar disorder.","date":"2006","source":"Molecular psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/16819533","citation_count":91,"is_preprint":false},{"pmid":"17449450","id":"PMC_17449450","title":"Are some genetic risk factors common to schizophrenia, bipolar disorder and depression? Evidence from DISC1, GRIK4 and NRG1.","date":"2007","source":"Neurotoxicity research","url":"https://pubmed.ncbi.nlm.nih.gov/17449450","citation_count":54,"is_preprint":false},{"pmid":"18824690","id":"PMC_18824690","title":"A common variant in the 3'UTR of the GRIK4 glutamate receptor gene affects transcript abundance and protects against bipolar disorder.","date":"2008","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/18824690","citation_count":53,"is_preprint":false},{"pmid":"22203159","id":"PMC_22203159","title":"Genetic ablation of the GluK4 kainate receptor subunit causes anxiolytic and antidepressant-like behavior in mice.","date":"2011","source":"Behavioural brain research","url":"https://pubmed.ncbi.nlm.nih.gov/22203159","citation_count":48,"is_preprint":false},{"pmid":"12052549","id":"PMC_12052549","title":"Sphingomonas sp. strain KA1, carrying a carbazole dioxygenase gene homologue, degrades chlorinated dibenzo-p-dioxins in soil.","date":"2002","source":"FEMS microbiology letters","url":"https://pubmed.ncbi.nlm.nih.gov/12052549","citation_count":46,"is_preprint":false},{"pmid":"8843098","id":"PMC_8843098","title":"The effect of chronic haloperidol treatment on glutamate receptor subunit (GluR1, GluR2, KA1, KA2, NR1) mRNAs and glutamate binding protein mRNA in rat forebrain.","date":"1996","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/8843098","citation_count":45,"is_preprint":false},{"pmid":"26446216","id":"PMC_26446216","title":"Increased Dosage of High-Affinity Kainate Receptor Gene grik4 Alters Synaptic Transmission and Reproduces Autism Spectrum Disorders Features.","date":"2015","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/26446216","citation_count":44,"is_preprint":false},{"pmid":"16325263","id":"PMC_16325263","title":"Association study of polymorphisms in the GluR7, KA1 and KA2 kainate receptor genes (GRIK3, GRIK4, GRIK5) with schizophrenia.","date":"2005","source":"Psychiatry research","url":"https://pubmed.ncbi.nlm.nih.gov/16325263","citation_count":40,"is_preprint":false},{"pmid":"23357115","id":"PMC_23357115","title":"The GluK4 kainate receptor subunit regulates memory, mood, and excitotoxic neurodegeneration.","date":"2013","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/23357115","citation_count":39,"is_preprint":false},{"pmid":"24449200","id":"PMC_24449200","title":"1p34.3 deletion involving GRIK3: Further clinical implication of GRIK family glutamate receptors in the pathogenesis of developmental delay.","date":"2013","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/24449200","citation_count":31,"is_preprint":false},{"pmid":"29949767","id":"PMC_29949767","title":"Increased Grik4 Gene Dosage Causes Imbalanced Circuit Output and Human Disease-Related Behaviors.","date":"2018","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/29949767","citation_count":30,"is_preprint":false},{"pmid":"27879374","id":"PMC_27879374","title":"Molecular determinants of KA1 domain-mediated autoinhibition and phospholipid activation of MARK1 kinase.","date":"2016","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/27879374","citation_count":25,"is_preprint":false},{"pmid":"25303296","id":"PMC_25303296","title":"GRIK4 polymorphism and its association with antidepressant response in depressed patients: a meta-analysis.","date":"2014","source":"Pharmacogenomics","url":"https://pubmed.ncbi.nlm.nih.gov/25303296","citation_count":24,"is_preprint":false},{"pmid":"28284346","id":"PMC_28284346","title":"AMPA, NMDA and kainate glutamate receptor subunits are expressed in human peripheral blood mononuclear cells (PBMCs) where the expression of GluK4 is altered by pregnancy and GluN2D by depression in pregnant women.","date":"2017","source":"Journal of neuroimmunology","url":"https://pubmed.ncbi.nlm.nih.gov/28284346","citation_count":24,"is_preprint":false},{"pmid":"11000488","id":"PMC_11000488","title":"KA1-like kainate receptor subunit immunoreactivity in neurons and glia using a novel anti-peptide antibody.","date":"2000","source":"Brain research. Molecular brain research","url":"https://pubmed.ncbi.nlm.nih.gov/11000488","citation_count":23,"is_preprint":false},{"pmid":"22980146","id":"PMC_22980146","title":"AKAP13, CACNA1, GRIK4 and GRIA1 genetic variations may be associated with haloperidol efficacy during acute treatment.","date":"2012","source":"European neuropsychopharmacology : the journal of the European College of Neuropsychopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/22980146","citation_count":22,"is_preprint":false},{"pmid":"26139080","id":"PMC_26139080","title":"The role of GRIK4 gene in treatment-resistant depression.","date":"2015","source":"Genetics research","url":"https://pubmed.ncbi.nlm.nih.gov/26139080","citation_count":21,"is_preprint":false},{"pmid":"30099988","id":"PMC_30099988","title":"Structural Basis for MARK1 Kinase Autoinhibition by Its KA1 Domain.","date":"2018","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/30099988","citation_count":20,"is_preprint":false},{"pmid":"7527545","id":"PMC_7527545","title":"The genes encoding the glutamate receptor subunits KA1 and KA2 (GRIK4 and GRIK5) are located on separate chromosomes in human, mouse, and rat.","date":"1994","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/7527545","citation_count":19,"is_preprint":false},{"pmid":"19114596","id":"PMC_19114596","title":"Proteolytic fragments of laminin promote excitotoxic neurodegeneration by up-regulation of the KA1 subunit of the kainate receptor.","date":"2008","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/19114596","citation_count":19,"is_preprint":false},{"pmid":"22222462","id":"PMC_22222462","title":"Failure to replicate influence of GRIK4 and GNB3 polymorphisms on treatment outcome in major depression.","date":"2012","source":"Neuropsychobiology","url":"https://pubmed.ncbi.nlm.nih.gov/22222462","citation_count":18,"is_preprint":false},{"pmid":"10973593","id":"PMC_10973593","title":"Developmental profile of kainate receptor subunit KA1 revealed by Cre expression in YAC transgenic mice.","date":"2000","source":"Brain research","url":"https://pubmed.ncbi.nlm.nih.gov/10973593","citation_count":17,"is_preprint":false},{"pmid":"27222927","id":"PMC_27222927","title":"Influence of GRIK4 genetic variants on the electroconvulsive therapy response.","date":"2016","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/27222927","citation_count":13,"is_preprint":false},{"pmid":"26039276","id":"PMC_26039276","title":"KA1-targeted regulatory domain mutations activate Chk1 in the absence of DNA damage.","date":"2015","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/26039276","citation_count":12,"is_preprint":false},{"pmid":"8963683","id":"PMC_8963683","title":"Contrasting effects of electroconvulsive shock on mRNAs encoding the high affinity kainate receptor subunits (KA1 and KA2) and cyclophilin in the rat.","date":"1996","source":"Brain research","url":"https://pubmed.ncbi.nlm.nih.gov/8963683","citation_count":12,"is_preprint":false},{"pmid":"27524200","id":"PMC_27524200","title":"The Structure of a High-Affinity Kainate Receptor: GluK4 Ligand-Binding Domain Crystallized with Kainate.","date":"2016","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/27524200","citation_count":10,"is_preprint":false},{"pmid":"26615815","id":"PMC_26615815","title":"Optimization of crude oil degradation by Dietzia cinnamea KA1, capable of biosurfactant production.","date":"2015","source":"Journal of basic microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/26615815","citation_count":10,"is_preprint":false},{"pmid":"30510197","id":"PMC_30510197","title":"Chk1 KA1 domain auto-phosphorylation stimulates biological activity and is linked to rapid proteasomal degradation.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30510197","citation_count":9,"is_preprint":false},{"pmid":"18289755","id":"PMC_18289755","title":"No genetic association between polymorphisms in the kainate-type glutamate receptor gene, GRIK4, and schizophrenia in the Chinese population.","date":"2008","source":"Progress in neuro-psychopharmacology & biological psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/18289755","citation_count":8,"is_preprint":false},{"pmid":"38590740","id":"PMC_38590740","title":"GRIK phosphorylates and activates KIN10 which also promotes its degradation.","date":"2024","source":"Frontiers in plant science","url":"https://pubmed.ncbi.nlm.nih.gov/38590740","citation_count":7,"is_preprint":false},{"pmid":"29243543","id":"PMC_29243543","title":"A kainate receptor GluK4 deletion, protective against bipolar disorder, is associated with enhanced cognitive performance across diagnoses in the TwinsUK cohort.","date":"2018","source":"The world journal of biological psychiatry : the official journal of the World Federation of Societies of Biological Psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/29243543","citation_count":7,"is_preprint":false},{"pmid":"22489103","id":"PMC_22489103","title":"Synaptic Pattern of KA1 and KA2 upon the Direction-Selective Ganglion Cells in Developing and Adult Mouse Retina.","date":"2012","source":"Acta histochemica et cytochemica","url":"https://pubmed.ncbi.nlm.nih.gov/22489103","citation_count":7,"is_preprint":false},{"pmid":"31083176","id":"PMC_31083176","title":"GRIK4 and GRM7 gene may be potential indicator of venlafaxine treatment reponses in Chinese of Han ethnicity.","date":"2019","source":"Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/31083176","citation_count":6,"is_preprint":false},{"pmid":"32245654","id":"PMC_32245654","title":"Impact of GRIK4 gene polymorphisms on cognitive dysfunction in patients with major depression.","date":"2020","source":"Revue neurologique","url":"https://pubmed.ncbi.nlm.nih.gov/32245654","citation_count":5,"is_preprint":false},{"pmid":"18607094","id":"PMC_18607094","title":"Crystallization and preliminary X-ray diffraction studies of a novel ferredoxin involved in the dioxygenation of carbazole by Novosphingobium sp. KA1.","date":"2008","source":"Acta crystallographica. Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/18607094","citation_count":5,"is_preprint":false},{"pmid":"28583584","id":"PMC_28583584","title":"Common variants in GRIK4 and major depressive disorder: An association study in the Chinese Han population.","date":"2017","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/28583584","citation_count":4,"is_preprint":false},{"pmid":"20516607","id":"PMC_20516607","title":"Crystallization and preliminary X-ray diffraction studies of a ferredoxin reductase component of carbazole 1,9a-dioxygenase from Novosphingobium sp. KA1.","date":"2010","source":"Acta crystallographica. Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/20516607","citation_count":4,"is_preprint":false},{"pmid":"30089246","id":"PMC_30089246","title":"KA1 Domains: Unity in Mechanistic Diversity.","date":"2018","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/30089246","citation_count":3,"is_preprint":false},{"pmid":"21045300","id":"PMC_21045300","title":"Crystallization and preliminary X-ray diffraction studies of a terminal oxygenase of carbazole 1,9a-dioxygenase from Novosphingobium sp. KA1.","date":"2010","source":"Acta crystallographica. Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/21045300","citation_count":3,"is_preprint":false},{"pmid":"38969617","id":"PMC_38969617","title":"SARS-CoV-2-derived protein Orf9b enhances MARK2 activity via interaction with the autoinhibitory KA1 domain.","date":"2024","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/38969617","citation_count":1,"is_preprint":false},{"pmid":"21113098","id":"PMC_21113098","title":"Expression of KA1 kainate receptor subunit in the substantia gelatinosa of the trigeminal subnucleus caudalis in mice.","date":"2010","source":"Journal of veterinary science","url":"https://pubmed.ncbi.nlm.nih.gov/21113098","citation_count":0,"is_preprint":false},{"pmid":"40816457","id":"PMC_40816457","title":"Mitosis Localization Signal (MLS) extends KA1 and regulates MELK kinase localization to plasma membrane and activity in Xenopus embryo.","date":"2025","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/40816457","citation_count":0,"is_preprint":false},{"pmid":"25736111","id":"PMC_25736111","title":"[Role of KA1 receptor in excitotoxic neurodegeneration in mouse hippocampus triggered by kainic acid- or tunicamycin-induced endoplasmic reticulum stress].","date":"2015","source":"Nan fang yi ke da xue xue bao = Journal of Southern Medical University","url":"https://pubmed.ncbi.nlm.nih.gov/25736111","citation_count":0,"is_preprint":false},{"pmid":"10730851","id":"PMC_10730851","title":"Linkage mapping of the interleukin 1beta converting enzyme (Il1bc) and the glutamate receptor subunit KA1 (Grik4) genes to rat chromosome 8.","date":"1998","source":"Folia biologica","url":"https://pubmed.ncbi.nlm.nih.gov/10730851","citation_count":0,"is_preprint":false},{"pmid":"8395199","id":"PMC_8395199","title":"Epithelial cell membrane specific, novel monoclonal antibody KA-1.","date":"1993","source":"Journal of dermatological science","url":"https://pubmed.ncbi.nlm.nih.gov/8395199","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.02.07.634209","title":"Nim1-related kinases regulate septin organization and cytokinesis by modulating Hof1 at the cell division site","date":"2025-02-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.07.634209","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":22650,"output_tokens":3472,"usd":0.060015,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10612,"output_tokens":2981,"usd":0.063793,"stage2_stop_reason":"end_turn"},"total_usd":0.123808,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"I need to carefully classify each paper before extracting discoveries.\n\n**Classification:**\n- Papers [1,3,4,5,10,15,18,19,23,25,31,35,36,38]: GRIK4/KA1 glutamate receptor gene association studies — mostly expression/association, not mechanistic\n- Papers [2,8,27]: KA1 mRNA expression changes — not mechanistic about protein function\n- Papers [6,9,11,13]: Mouse Grik4 KO/OE functional studies — relevant mechanistic\n- Papers [17,22,24,28,34,43,45,46]: KA1 kainate receptor protein studies — relevant mechanistic\n- Papers [12]: GRIK3 paper mentioning GRIK4 briefly — mostly non-mechanistic\n- Papers [7,29,37,38,39,41]: Bacterial/microbial KA1 strain — SYMBOL COLLISION, skip\n- Papers [14,20,26,30,40,42,44,48]: KA1 domain of MARK/Chk1/MELK kinases — SYMBOL COLLISION (different protein), skip\n- Papers [32]: GRIK in plants (Arabidopsis GRIK1/2) — SYMBOL COLLISION, skip\n- Papers [33,16]: Some mechanistic relevance\n- Paper [47]: Monoclonal antibody KA-1 against keratinocytes — SYMBOL COLLISION, skip\n\nNow extracting mechanistic discoveries:\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"KA1/GluK4 subunit immunoreactivity was localized by immunohistochemistry and electron microscopy to dendritic structures in the CA3 area of the hippocampus (postsynaptic to commissural-associational fibers rather than mossy fiber terminals), CA1 pyramidal cell apical dendrites, cortical layer V pyramidal neurons, GABAergic interneurons, Purkinje cells, and glial cells (oligodendrocytes and astrocytes), indicating a broader CNS distribution than previously appreciated.\",\n      \"method\": \"Immunohistochemistry with anti-peptide antibody to C-terminus of KA1, electron microscopy, cell fractionation\",\n      \"journal\": \"Brain research. Molecular brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by EM and immunohistochemistry with novel validated antibody, single lab, two orthogonal methods\",\n      \"pmids\": [\"11000488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The KA1 (GluK4) gene promoter drives expression broadly throughout the developing brain during early postnatal development, becoming restricted mainly to hippocampal CA3 pyramidal cells and dentate gyrus granule cells in the adult brain, as established by YAC transgenic Cre-reporter mice.\",\n      \"method\": \"YAC transgenic mice expressing Cre from KA1 gene locus, Cre immunohistochemistry, X-gal staining in double transgenic KA1-Cre/lacZ reporter mice\",\n      \"journal\": \"Brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct in vivo reporter system with two orthogonal readouts, single lab\",\n      \"pmids\": [\"10973593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Proteolytic fragments of laminin, generated via tPA-dependent plasmin activity, up-regulate the KA1 subunit of the kainate receptor in hippocampus following kainate injection. This KA1 up-regulation is required for excitotoxic neurodegeneration: laminin gamma1 KO and tPA KO mice both lack KA1 up-regulation and are resistant to kainate-induced neuronal death. Infusion of plasmin-digested laminin-1 restores KA1 up-regulation and neurodegeneration. Anti-KA1 antibody protects against kainate-induced neuronal death both in vitro and in vivo.\",\n      \"method\": \"Conditional hippocampal laminin gamma1 KO mice, tPA KO mice, intrahippocampal laminin fragment infusion, anti-KA1 antibody neutralization, in vitro and in vivo neurodegeneration assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple KO models, rescue experiment, antibody neutralization, in vitro and in vivo convergent results in single study\",\n      \"pmids\": [\"19114596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Genetic ablation of GluK4 (Grik4 knockout mice) produces anxiolytic and antidepressant-like phenotypes (elevated zero maze, marble burying, novelty-induced suppression of feeding, forced swim test, sucrose preference). GluK4 expression is restricted to CA3 hippocampus and dentate gyrus in forebrain. Grik4 KO impairs mossy fiber long-term potentiation, likely through loss of kainate receptor modulation of presynaptic mossy fiber axon excitability.\",\n      \"method\": \"Grik4 knockout mice, behavioral assays (elevated zero maze, marble burying, novelty-induced suppression of feeding, forced swim test, sucrose preference test), mossy fiber LTP electrophysiology\",\n      \"journal\": \"Behavioural brain research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with multiple behavioral readouts and synaptic electrophysiology, multiple orthogonal methods\",\n      \"pmids\": [\"22203159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GluK4 knockout mice show impaired spatial memory acquisition and recall in Morris water maze, marked hyperactivity, and impaired pre-pulse inhibition. GluK4 KO mice are robustly neuroprotected in CA3 following intrahippocampal kainate injection and throughout the hippocampus following hypoxia-ischemia. Biochemical analysis suggests GluK4 mediates excitotoxicity through the JNK signaling pathway.\",\n      \"method\": \"GluK4 knockout mice, Morris water maze, pre-pulse inhibition, intrahippocampal kainate injection, hypoxia-ischemia model, Western blot analysis of JNK pathway\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with multiple orthogonal behavioral and neurodegeneration readouts plus biochemical pathway analysis\",\n      \"pmids\": [\"23357115\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Forebrain overexpression of grik4 in mice causes social impairment, enhanced anxiety, and depressive states, accompanied by more efficient synaptic information transfer through the hippocampal trisynaptic circuit, demonstrating that increased GluK4 dosage alters synaptic transmission and produces autism spectrum disorder-related behavioral features.\",\n      \"method\": \"Grik4 forebrain-overexpressing transgenic mice, behavioral assays, hippocampal slice electrophysiology of trisynaptic circuit\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain-of-function transgenic model with multiple behavioral readouts and direct electrophysiological measurement of synaptic transmission\",\n      \"pmids\": [\"26446216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The X-ray crystal structure of the GluK4 ligand-binding domain (LBD) bound to kainate was solved at 2.05 Å resolution. Binding-site residues in GluK4 are most similar to AMPA receptor subfamily, but domain closure and D1-D2 interlobe contacts induced by kainate are similar to low-affinity kainate receptor GluK1, providing a structural explanation for the high kainate binding affinity of GluK4-LBD.\",\n      \"method\": \"X-ray crystallography at 2.05 Å, thermofluor assay, radiolabel binding affinity assays\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structure validated by binding affinity data, multiple orthogonal methods\",\n      \"pmids\": [\"27524200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Mild gain of Grik4 dosage in mouse forebrain enhances synaptic transmission and causes a persistent imbalance of inhibitory and excitatory activity, disturbing circuits responsible for main amygdala outputs. These changes in glutamatergic activity are reversible when Grik4 levels are normalized.\",\n      \"method\": \"Grik4 forebrain-overexpressing transgenic mice, in vivo electrophysiology, circuit analysis of amygdala outputs, normalization of Grik4 expression\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain-of-function model with electrophysiological circuit analysis and rescue by normalization of gene dosage\",\n      \"pmids\": [\"29949767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A deletion variant in the 3' UTR of GRIK4 is associated with protection against bipolar disorder. Expression studies showed that deletion-carrying mRNA transcripts were relatively more abundant, suggesting the protective effect is mediated through increased kainate receptor expression, possibly due to differences in RNA secondary structure between insertion and deletion alleles.\",\n      \"method\": \"Case-control genetic study with replication, mRNA expression analysis of variant carriers\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — expression difference shown in carriers but mechanism (RNA secondary structure effect) is postulated not directly demonstrated; single lab\",\n      \"pmids\": [\"18824690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"KA1 subunit mRNA and protein are expressed in the substantia gelatinosa of the trigeminal subnucleus caudalis, with expression levels significantly higher in juvenile than adult mice, suggesting an age-dependent role in nociceptive processing.\",\n      \"method\": \"RT-PCR, Western blot, immunohistochemistry in juvenile, prepubescent, and adult mice\",\n      \"journal\": \"Journal of veterinary science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — descriptive localization and quantitative expression without functional manipulation, single lab\",\n      \"pmids\": [\"21113098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Up-regulation of KA1 receptor following intrahippocampal kainate or tunicamycin (ER stress inducer) injection correlates with neuronal death and elevated ER stress marker P-eIF2α, suggesting KA1 participates in transmitting apoptotic signals leading to ER dysfunction and neurodegeneration.\",\n      \"method\": \"Intrahippocampal microinjection of kainate or tunicamycin in mice, FJB staining for cell death, immunofluorescence for KA1 and P-eIF2α\",\n      \"journal\": \"Nan fang yi ke da xue xue bao\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — correlative immunofluorescence without direct manipulation of KA1; single lab, single method\",\n      \"pmids\": [\"25736111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"KA1 and KA2 kainate receptor subunits are present on the dendritic arbors of direction-selective retinal ganglion cells (DS-RGCs) in both developing and adult mouse retina, but no asymmetric distribution was found that would predict direction selectivity.\",\n      \"method\": \"Immunocytochemistry, Lucifer yellow injection for DS-RGC morphology, confocal microscopy\",\n      \"journal\": \"Acta histochemica et cytochemica\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — localization study only, negative result for asymmetry, no functional manipulation\",\n      \"pmids\": [\"22489103\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GluK4 (GRIK4) is a high-affinity kainate-type ionotropic glutamate receptor subunit whose ligand-binding domain crystal structure shows AMPA-like binding-site residues with GluK1-like domain closure explaining high kainate affinity; it is expressed predominantly in hippocampal CA3 and dentate gyrus in adult brain, where it regulates mossy fiber LTP and modulates presynaptic excitability, and its loss (KO mice) produces anxiolytic, antidepressant-like, and neuroprotective phenotypes while its gain (forebrain overexpression) enhances excitatory/inhibitory balance, disrupts amygdala circuit output, and produces autism/schizophrenia-related behaviors; additionally, tPA-dependent laminin proteolysis up-regulates KA1 subunit levels in hippocampus to drive excitotoxic neurodegeneration, an effect blocked by anti-KA1 antibody.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GRIK4 encodes GluK4 (KA1), a high-affinity kainate-type ionotropic glutamate receptor subunit that shapes excitatory transmission in the hippocampal trisynaptic circuit and sets the threshold for glutamate-driven excitotoxicity [#3, #4]. Structurally, its ligand-binding domain combines AMPA-receptor-like binding-site residues with GluK1-like domain closure and D1-D2 interlobe contacts, accounting for its high kainate affinity [#6]. In the adult forebrain GluK4 expression is restricted largely to CA3 pyramidal cells and dentate gyrus granule cells, where the subunit modulates presynaptic mossy fiber excitability and is required for mossy fiber long-term potentiation [#1, #3]. GluK4 dosage bidirectionally controls circuit function: loss of the gene produces anxiolytic, antidepressant-like, and neuroprotective phenotypes along with impaired spatial memory and pre-pulse inhibition [#3, #4], whereas forebrain overexpression enhances synaptic information transfer through the trisynaptic circuit, produces a reversible excitatory/inhibitory imbalance that disrupts amygdala output, and generates autism- and depression-related behaviors [#5, #7]. GluK4 also transduces injury signals: its protein levels are up-regulated in hippocampus through tPA/plasmin-dependent proteolysis of laminin, an event required for kainate-induced excitotoxic neurodegeneration and blocked by anti-KA1 antibody, with downstream signaling through the JNK pathway [#2, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing where the KA1/GluK4 subunit resides was the first step toward assigning it a circuit role; immunolocalization showed a broader CNS distribution than expected and a postsynaptic position in CA3.\",\n      \"evidence\": \"Anti-peptide antibody immunohistochemistry and electron microscopy across hippocampus, cortex, cerebellum and glia\",\n      \"pmids\": [\"11000488\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Localization alone does not establish a functional or synaptic role\", \"Subunit composition of native receptors at these sites not defined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defining the developmental expression program clarified that GluK4 becomes restricted to the CA3/dentate region in the adult, focusing later functional studies on the trisynaptic circuit.\",\n      \"evidence\": \"YAC transgenic Cre-reporter mice with Cre immunohistochemistry and X-gal staining\",\n      \"pmids\": [\"10973593\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reporter expression may not capture all sites of endogenous protein\", \"Functional consequence of restriction not addressed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Connecting GluK4 to injury signaling, this work showed that tPA/plasmin-generated laminin fragments up-regulate KA1 and that this up-regulation is causally required for excitotoxic neurodegeneration.\",\n      \"evidence\": \"Conditional laminin gamma1 KO and tPA KO mice, laminin fragment infusion rescue, and anti-KA1 antibody neutralization in vitro and in vivo\",\n      \"pmids\": [\"19114596\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism linking laminin fragments to KA1 transcription/translation not defined\", \"Downstream death pathway not resolved here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"A human genetic association linked GRIK4 expression level to bipolar disorder risk, raising the possibility that receptor dosage influences mood.\",\n      \"evidence\": \"Case-control genetic study with replication plus mRNA expression analysis of 3' UTR deletion carriers\",\n      \"pmids\": [\"18824690\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"RNA secondary structure mechanism is postulated, not demonstrated\", \"No causal link between the variant and circuit phenotype shown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Loss-of-function genetics tested GluK4's behavioral and synaptic role, showing it is needed for mossy fiber LTP and that its absence is anxiolytic and antidepressant-like.\",\n      \"evidence\": \"Grik4 knockout mice with a battery of behavioral assays and mossy fiber LTP electrophysiology\",\n      \"pmids\": [\"22203159\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of presynaptic excitability modulation inferred, not directly measured\", \"Cell-type-specific contributions not separated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extending the KO phenotype, this work tied GluK4 to spatial memory, sensorimotor gating, and—critically—excitotoxic vulnerability via the JNK pathway.\",\n      \"evidence\": \"Grik4 KO mice in Morris water maze, pre-pulse inhibition, intrahippocampal kainate and hypoxia-ischemia models, with Western analysis of JNK signaling\",\n      \"pmids\": [\"23357115\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical coupling of GluK4 to JNK not demonstrated\", \"Whether neuroprotection is cell-autonomous unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Gain-of-function genetics established that increased GluK4 dosage is itself pathogenic, enhancing trisynaptic transmission and producing autism- and mood-related behaviors.\",\n      \"evidence\": \"Grik4 forebrain-overexpressing transgenic mice with behavioral assays and hippocampal slice electrophysiology\",\n      \"pmids\": [\"26446216\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of enhanced transmission not dissected\", \"Relationship to human dosage variation not established\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"The crystal structure answered why GluK4 binds kainate with high affinity, revealing AMPA-like binding residues paired with GluK1-like domain closure.\",\n      \"evidence\": \"X-ray crystallography of the GluK4 LBD bound to kainate at 2.05 Å with thermofluor and radioligand binding\",\n      \"pmids\": [\"27524200\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length receptor and gating not addressed\", \"Heteromeric assembly behavior not structurally defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Refining the dosage model, mild Grik4 overexpression was shown to cause a reversible excitatory/inhibitory imbalance disrupting amygdala output, demonstrating circuit-level reversibility.\",\n      \"evidence\": \"Grik4 forebrain-overexpressing transgenic mice with in vivo electrophysiology, amygdala circuit analysis, and normalization of gene dosage\",\n      \"pmids\": [\"29949767\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Synaptic locus of the imbalance not pinpointed\", \"Translation to therapeutic dosage modulation untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GluK4 dosage and laminin/tPA-driven up-regulation are coupled mechanistically to JNK- and ER-stress-dependent death versus circuit-level behavioral outcomes remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct molecular link between GluK4 and JNK or ER-stress effectors established\", \"Subunit composition of native GluK4-containing receptors in each circuit undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [3, 6]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [3, 5]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"complexes\": [\"kainate receptor\"],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}