{"gene":"EIF2AK4","run_date":"2026-06-09T23:54:42","timeline":{"discoveries":[{"year":2000,"finding":"GCN2 contains a bipartite tRNA-binding domain composed of the HisRS-related domain plus a C-terminal ribosome-binding segment (C-term); the combined HisRS+C-term segment binds the isolated kinase domain in vitro, and uncharged tRNA impedes this inhibitory intramolecular interaction, thereby activating the kinase moiety. Aminoacylation of tRNA weakens its interaction with GCN2, and an activating mutation (E803V) that weakens PK-C-term association greatly enhanced tRNA binding.","method":"In vitro binding assays, tRNA binding assays with aminoacylated vs. deacylated tRNAs, activating mutant analysis, domain dissection","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified domains, mutagenesis, and multiple orthogonal binding assays in a focused mechanistic study","pmids":["10983975"],"is_preprint":false},{"year":1990,"finding":"GCN2 acts as a protein kinase to stimulate GCN4 expression; substitution of the conserved lysine in the kinase domain abolished both GCN2 regulatory function in vivo and autophosphorylation in vitro. The HisRS-related sequences and C-terminal segment flanking the kinase domain are positive-acting regulatory domains required for physiological substrate recognition or lowering the threshold for uncharged tRNA activation.","method":"In vitro autophosphorylation assay, in vivo reporter (GCN4-lacZ), site-directed mutagenesis, deletion analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — catalytic dead mutant abolishes both in vitro kinase activity and in vivo function; replicated across multiple domain mutations","pmids":["2188100"],"is_preprint":false},{"year":1996,"finding":"The HisRS-related sequences of GCN2 are required for phosphorylation of eIF-2α in vitro; mutations in this domain that block the general amino acid control pathway in vivo also greatly reduce eIF-2α phosphorylation in a cell-free assay using recombinant eIF-2α substrate (phosphorylation requires Ser-51 of eIF-2α).","method":"In vitro kinase assay with purified recombinant eIF-2α substrate, HisRS-domain point mutations","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro kinase assay with mutagenesis, correlated with in vivo phenotype","pmids":["8798780"],"is_preprint":false},{"year":1991,"finding":"GCN2 physically associates with 60S ribosomal subunits and polysomes in yeast cell extracts; it can be dissociated from 60S subunits by 0.5 M KCl. The extreme C-terminal segment of GCN2 is essential for ribosome interaction, and this segment is also required for GCN4 translational activation in vivo.","method":"Sucrose gradient sedimentation, nondenaturing gel electrophoresis, ribosome dissociation experiments, C-terminal deletion analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct fractionation experiments with functional validation by deletion mutagenesis; replicated across multiple conditions","pmids":["2038314"],"is_preprint":false},{"year":2000,"finding":"Mouse GCN2, a mammalian homologue of yeast GCN2, phosphorylates recombinant eIF-2α in vitro requiring the kinase catalytic domain and HisRS-related sequences, and the phosphorylation requires Ser-51 of eIF-2α. Three mouse GCN2 isoforms are encoded by a single gene with differential N-terminal sequences.","method":"In vitro kinase assay with recombinant eIF-2α, expression of mGCN2 in yeast, Ser-51 mutagenesis","journal":"Genetics","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with Ser-51 mutagenesis and complementary in vivo yeast system","pmids":["10655230"],"is_preprint":false},{"year":2005,"finding":"Crystal structures of the GCN2 protein kinase domain (wild-type and R794G mutant) reveal that autoinhibition results from stabilization of a closed conformation that restricts ATP binding. The R794G mutation increases hinge-region flexibility between N- and C-lobes, enhancing ATP binding and hydrolysis, and provides a model for how tRNA binding to the HisRS domain remodels the hinge for kinase activation.","method":"X-ray crystallography of apo and ATP/AMPPNP-bound kinase domain; biochemical validation of R794G activating mutant","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures of both wild-type and activating mutant with functional correlation","pmids":["15964839"],"is_preprint":false},{"year":2003,"finding":"The TOR pathway negatively regulates GCN2 in yeast by promoting phosphorylation of Ser-577 in GCN2, which reduces tRNA binding activity and inhibits kinase function. Rapamycin-induced TOR inhibition leads to Ser-577 dephosphorylation via TAP42-regulated type 2A-related phosphatases, thereby activating GCN2 and increasing eIF2α phosphorylation and GCN4 translation.","method":"Phosphorylation-site mutagenesis (S577A), rapamycin treatment, GCN4-lacZ reporter, eIF2α phosphorylation assays, TAP42 genetic analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — site-directed mutagenesis combined with pharmacological and genetic epistasis across multiple readouts","pmids":["12654728"],"is_preprint":false},{"year":2005,"finding":"GCN2 and PKR phosphorylate eIF2α on Ser-51; residues flanking Ser-51 (Glu-49) and a remote surface residue Asp-83 in the K79GYID83 motif are critical for kinase-substrate recognition. Ala substitution of Asp-83 eliminates phosphorylation by both GCN2 and PKR in vivo and in vitro, establishing that distal surface residues contribute to substrate recognition. Separately, mutations that block translational regulation but not Ser-51 phosphorylation impair eIF2B binding to phospho-eIF2α.","method":"In vivo and in vitro phosphorylation assays, eIF2α mutagenesis, eIF2B binding assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with systematic mutagenesis correlated with in vivo function","pmids":["15798194"],"is_preprint":false},{"year":2007,"finding":"A conserved intermolecular salt bridge between an Arg and Asp/Glu residue (equivalent to Arg-262/Asp-266 in PKR) at the kinase domain dimer interface is essential for GCN2 (and PKR, PERK) activity. Single charge-reversal mutations in either residue abolish kinase function in yeast cells and in vitro; double mutations restoring salt bridge with opposite polarity restore function, demonstrating that dimerization via this interface is required for eIF2α kinase activation.","method":"Site-directed mutagenesis, in vivo yeast functional assay, in vitro kinase assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — charge-swap mutagenesis with both in vitro and in vivo validation across three eIF2α kinases","pmids":["17202131"],"is_preprint":false},{"year":1999,"finding":"GCN2 forms a complex with the molecular chaperone Hsp90 both in vitro and in vivo in yeast. Hsp90 inhibitors (geldanamycin, macbecin I) enhance GCN2-Hsp90 association and inhibit GCN2 kinase activity in vitro; in vivo, macbecin I strongly reduces GCN2 protein levels. Hsp90 cochaperones Cdc37, Sti1, and Sba1 are required for the amino acid starvation response, indicating Hsp90 is required for GCN2 maturation and regulation.","method":"Co-immunoprecipitation in vitro and in vivo, Hsp90 inhibitor treatment, temperature-sensitive Hsp90 mutant analysis, GCN4-lacZ reporter","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP in vitro and in vivo combined with pharmacological and genetic validation","pmids":["10567567"],"is_preprint":false},{"year":2019,"finding":"Human GCN2 is potently stimulated by ribosomes and, to a lesser extent, by uncharged tRNA in a reconstituted in vitro system. The ribosomal P-stalk domain II of uL10 is the principal binding site for GCN2; the conserved 14-residue C-terminal tails of P1/P2 P-stalk proteins are also essential for GCN2 activation. HDX-MS showed conformational changes in both the HisRS-like and kinase domains of GCN2 upon P-stalk binding.","method":"In vitro reconstitution with purified components, HDX-MS, recombinant P-stalk complex binding assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified recombinant human GCN2 and P-stalk components, HDX-MS structural data, multiple orthogonal methods","pmids":["30804176"],"is_preprint":false},{"year":2002,"finding":"GCN2 is essential for eIF2α phosphorylation in response to amino acid deprivation in mammals. Gcn2-/- mice fail to induce eIF2α phosphorylation in leucine-deprived embryonic stem cells, and perfused livers from Gcn2-/- mice fail to show increased eIF2α phosphorylation or decreased eIF2B activity upon histidine limitation. Loss of GCN2 increases prenatal/neonatal mortality when mothers are fed amino acid-deficient diets.","method":"Gcn2 knockout mouse, eIF2α phosphorylation assay in ES cells and perfused liver, eIF2B activity assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with direct biochemical readout of substrate phosphorylation in multiple tissue systems","pmids":["12215525"],"is_preprint":false},{"year":2006,"finding":"Mammalian GCN2 is specifically activated in vitro by binding of two nonadjacent regions of Sindbis virus genomic RNA to its HisRS-related domain. Endogenous GCN2 is activated during Sindbis virus infection in cells. GCN2-/- mouse fibroblasts show increased permissiveness to Sindbis virus and VSV infection, and GCN2-/- mice are highly susceptible to intranasal SV infection with higher brain virus titers. Catalytically inactive GCN2-K618R fails to impair viral replication, and GCN2 inhibits SV replication by blocking early viral translation.","method":"In vitro RNA-binding and kinase activation assay, GCN2 knockout fibroblasts and mice, viral infection assays, kinase-dead mutant (K618R)","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro activation assay combined with genetic knockout in cells and in vivo, plus catalytic-dead mutant validation","pmids":["16601681"],"is_preprint":false},{"year":2005,"finding":"GCN2 regulates hippocampal synaptic plasticity and memory through modulation of ATF4/CREB pathway. In GCN2-/- mice, ATF4 expression is reduced and CREB activity is increased in the hippocampus, consistent with GCN2-activated eIF2α phosphorylation normally promoting ATF4 mRNA translation which antagonizes CREB.","method":"GCN2 knockout mouse, electrophysiology (LTP), behavioral testing (Morris water maze), ATF4 and CREB activity measurements","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with multiple orthogonal readouts (electrophysiology, behavior, molecular signaling) in a high-profile study","pmids":["16121183"],"is_preprint":false},{"year":2010,"finding":"Both amino acid and glucose deprivation activate GCN2 to upregulate ATF4 target genes involved in amino acid synthesis and transport in tumour cells. GCN2 activation and increased phospho-eIF2α are observed in human and mouse tumours; abrogation of GCN2 or ATF4 expression significantly inhibits tumour growth in vivo.","method":"GCN2 knockdown/overexpression, eIF2α phosphorylation assay, in vivo tumour growth experiments, ATF4 target gene expression analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function (knockdown) combined with in vivo tumour models and molecular pathway analysis","pmids":["20473272"],"is_preprint":false},{"year":2014,"finding":"Crystal structures of murine and yeast GCN2 C-terminal domains (CTDs) reveal an unusual interdigitated dimeric form; disruption of the dimeric form of murine CTD eliminates GCN2 translational control function. Despite shared core structure, murine GCN2 CTD does not stably associate with ribosomes whereas yeast GCN2 CTD does, indicating regulatory differences between yeast and mammalian GCN2.","method":"X-ray crystallography, dimerization-disrupting mutations with functional assays, ribosome association assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures of both yeast and murine CTDs combined with functional validation of dimerization mutants","pmids":["24719324"],"is_preprint":false},{"year":2014,"finding":"The GCN2 pseudokinase domain (YKD) directly interacts with the kinase domain (KD) to allosterically stimulate kinase activity in amino acid-starved cells. Substitutions in predicted helices αE and αI of the YKD impair GCN2 activation without reducing uncharged tRNA binding; αI substitutions identified as Gcd- (constitutively active) enhance YKD-KD interactions in vitro, while αE/αI Gcn- substitutions suppress this effect.","method":"Mutational analysis of YKD, in vitro YKD-KD interaction assay, in vivo GCN4-lacZ reporter, tRNA binding assays","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro domain interaction assay combined with systematic mutagenesis and in vivo functional readout","pmids":["24811037"],"is_preprint":false},{"year":2021,"finding":"Gcn2 phosphorylates the β-subunit of eIF2 to promote its association with eIF5, preventing spontaneous nucleotide exchange on eIF2 and restricting recycling of the initiator Met-tRNA-bound eIF2-GDP ternary complex in amino-acid-starved cells—a mechanism parallel to eIF2α phosphorylation-dependent eIF2B sequestration. Gcn2 also phosphorylates Gcn20 to antagonize formation of the Gcn2-stimulatory Gcn1-Gcn20 complex in a negative feedback loop.","method":"Quantitative phosphoproteomics, Co-immunoprecipitation, translation initiation assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — quantitative phosphoproteomics identifying novel substrates with biochemical validation of eIF2β-eIF5 interaction and Gcn20 feedback","pmids":["33743194"],"is_preprint":false},{"year":2011,"finding":"Yih1 (yeast) / IMPACT (mammalian) inhibits GCN2 by competing with GCN2 for binding to the GCN2 activator Gcn1 via its RWD domain. Gcn1 binding and GCN2 inhibition require residues Asp-102 and Glu-106 in helix 3 of the RWD domain. Yih1 also binds G-actin independently of Gcn1 binding, but actin binding is dispensable for GCN2 inhibition.","method":"Co-immunoprecipitation, in vitro binding assays, site-directed mutagenesis of Yih1 RWD domain, in vivo GCN4-lacZ reporter","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding assays combined with mutagenesis and in vivo functional validation","pmids":["21239490"],"is_preprint":false},{"year":2019,"finding":"In yeast, GCN2 activation by ribosome stalling (starvation-independent conditions) requires at least one P1/P2 P-stalk heterodimer tethered to uL10 of the ribosomal P-stalk, the tRNA- and ribosome-binding domains of Gcn2, and the positive effectors Gcn1/Gcn20. By contrast, amino acid starvation-induced GCN2 activation does not require tethered P1/P2 proteins, suggesting that uncharged tRNAs can substitute for the P-stalk in activating GCN2 at ribosomes with empty A-sites.","method":"Genetic analysis in yeast (P-stalk deletion mutants, GCN2 domain mutants, epistasis), eIF2α phosphorylation assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic genetic epistasis with multiple independent stalling conditions distinguishing two activation mechanisms","pmids":["37043534"],"is_preprint":false},{"year":2024,"finding":"Multiple mechanisms activate GCN2 depending on stress type: ribosomal collisions are essential for GCN2 activation by translational elongation inhibitors (stalling conditions), while direct association of GCN2 with uncharged tRNAs is the primary mechanism when amino acid depletion causes tRNA deacylation. Both mechanisms require the HisRS-like regulatory domain of GCN2. UV irradiation activates GCN2 via decreased amino acids and increased uncharged tRNAs rather than ribosome collisions.","method":"Domain mutagenesis, ribosome collision assays, tRNA deacylation assays, selective inhibitor treatment, eIF2α phosphorylation assays under multiple stress conditions","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic analysis distinguishing multiple mechanisms across diverse stress conditions with domain mutants","pmids":["38281137"],"is_preprint":false},{"year":2017,"finding":"Mutation of tRNA-binding site on GCN2 or deletion of Gcn1 abolishes GCN2 activation under all investigated stress conditions (amino acid starvation, UV irradiation, and oxidative stress) in fission yeast, indicating that tRNA binding to GCN2 is required for activation not only by starvation but also by other stresses.","method":"GCN2 tRNA-binding site mutagenesis, Gcn1 deletion, eIF2α phosphorylation assays under multiple stress conditions in S. pombe","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function analysis across multiple stresses, single lab with orthogonal stress conditions but no in vitro reconstitution","pmids":["28771613"],"is_preprint":false},{"year":2013,"finding":"GCN2 activation upon HIV-1 infection requires GCN2's interaction with HIV-1 integrase. GCN2 phosphorylates HIV-1 integrase in vitro at Ser-255 in the C-terminal domain, and the integrase active site is required for GCN2 to target this residue. HIV-1 lentiviral particles with S255 mutation (preventing phosphorylation) show increased infectivity and viral DNA integration; MLV infectivity is also higher in GCN2 knockout cells.","method":"In vitro kinase assay with HIV-1 integrase substrate, phosphorylation site mapping (mass spectrometry), site-directed mutagenesis (S255), GCN2 Co-IP with integrase, viral infectivity assays in GCN2 KO cells","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro kinase assay identifying novel substrate with mutagenesis of phosphorylation site and functional validation in cells","pmids":["28536474"],"is_preprint":false},{"year":2018,"finding":"Amino acid restriction triggers angiogenesis via the GCN2/ATF4 pathway, independently of hypoxia or HIF1α. Sulfur amino acid restriction promotes VEGF expression, EC migration and sprouting via GCN2/ATF4 signaling in vitro and increased capillary density in mouse skeletal muscle in vivo.","method":"GCN2 knockout/knockdown experiments, endothelial cell migration and sprouting assays, in vivo capillary density measurement, VEGF expression analysis, ATF4 pathway analysis","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function with multiple cellular and in vivo readouts establishing GCN2 as upstream regulator of VEGF/angiogenesis","pmids":["29570992"],"is_preprint":false},{"year":2023,"finding":"GCN2 phosphorylates FBXO22 in response to accumulation of uncharged tRNAs caused by amino acid depletion; phosphorylated FBXO22 translocates to the cytoplasm and ubiquitinates mTOR at Lys-2066 in a K27-linked manner, inhibiting mTORC1 kinase activity by preventing substrate recruitment. Mutation of mTOR Lys-2066 abolishes this regulation, rendering mTOR insensitive to amino acid starvation.","method":"In vitro kinase assay (GCN2→FBXO22 phosphorylation), ubiquitination assay, mTOR K2066 mutagenesis, cellular fractionation, mTORC1 substrate recruitment assay","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro kinase and ubiquitination reconstitution combined with mutagenesis of the target site and in vivo validation","pmids":["37979583"],"is_preprint":false},{"year":2016,"finding":"GCN2 (EIF2AK4) drives ATF4-dependent maturation and polarization of macrophages and MDSCs; myeloid-lineage deletion of GCN2 shifts macrophage/MDSC phenotype toward pro-inflammatory activation and promotes antitumor immunity in melanoma. ATF4 translation is a key downstream mediator of this effect.","method":"Myeloid-specific GCN2 conditional knockout, CyTOF mass cytometry, single-cell RNA-seq, ATF4 siRNA knockdown, transcription factor binding analysis","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with multiple orthogonal readouts (CyTOF, scRNA-seq, siRNA) establishing mechanistic pathway","pmids":["31836669"],"is_preprint":false},{"year":2021,"finding":"GCN2 directs keratinocyte collective cell migration during wound healing by maintaining intracellular free amino acids (particularly cysteine) and coordinating RAC1-GTP-driven reactive oxygen species generation, lamellipodia formation, and focal adhesion dynamics. GCN2 deletion or pharmacological inhibition significantly delays collective cell migration and wound closure in vitro and in vivo.","method":"GCN2 knockout cells and mice, pharmacological inhibition, wound scratch assay, RAC1-GTP pulldown, ROS measurement, transcriptomics, focal adhesion imaging","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic and pharmacological loss-of-function with multiple mechanistic readouts and in vivo validation","pmids":["34597669"],"is_preprint":false},{"year":2022,"finding":"GCN2 regulates expression of over 60 solute carrier (SLC) transporter genes including amino acid transporters; loss of GCN2 reduces amino acid import and levels in prostate cancer cells. Addition of essential amino acids or expression of SLC3A2 (4F2 heavy chain) partially restores growth following GCN2 loss, placing GCN2 upstream of SLC transporter expression for amino acid homeostasis.","method":"GCN2 knockout in prostate cancer cells, RNA-seq, CRISPR phenotypic screen, amino acid measurement, rescue experiments with amino acid supplementation and SLC3A2 overexpression, in vivo mouse models","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR KO with RNA-seq, CRISPR screen, metabolite measurements, and rescue experiments in vitro and in vivo","pmids":["36107759"],"is_preprint":false},{"year":2022,"finding":"GCN2 maintains proteostasis in hematopoietic stem cells (HSCs) by sensing amino acid levels and inhibiting protein synthesis via the eIF2α axis; GCN2 also inhibits Src-mediated AKT activation to repress mitochondrial OXPHOS. GCN2 deletion impairs HSC repopulation and regeneration capacity.","method":"GCN2 knockout mice, HSC functional assays (repopulation, transplantation), protein synthesis measurement, Src/AKT phosphorylation analysis","journal":"Cell stem cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple mechanistic readouts (proteostasis, signaling pathway, function) in primary cells","pmids":["35803229"],"is_preprint":false},{"year":2013,"finding":"GCN2 promotes macrophage inflammatory cytokine production (IL-6, IL-12) in response to LPS under amino acid-deficient conditions; GCN2 knockout macrophages show significantly reduced cytokine gene expression after LPS stimulation. Monocytic-lineage GCN2 knockout mice show reduced inflammatory responses and significantly decreased mortality in a lethal LPS septicemia model.","method":"GCN2 knockout macrophages and monocyte-specific conditional knockout mice, LPS challenge, cytokine measurement, in vivo septicemia model","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO at cell and whole-animal level with defined molecular and survival phenotypes","pmids":["24248597"],"is_preprint":false},{"year":2021,"finding":"GCN2 interacts with NRF2 and decreases NRF2 expression in a KEAP1-dependent manner. Activation of GCN2 by halofuginone or leucine deprivation decreases NRF2 expression in hepatocytes by increasing GSK-3β activity. This defines a GCN2→GSK-3β→KEAP1→NRF2 regulatory axis in oxidative stress response.","method":"Co-immunoprecipitation (GCN2-NRF2), GCN2 knockdown (AAV8-shGcn2), pharmacological GCN2 activation and inhibition, GSK-3β activity assay, NRF2 expression analysis, in vivo hepatic steatosis models","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP plus pharmacological and in vivo genetic approaches, single lab, mechanistic follow-up incomplete","pmids":["34954499"],"is_preprint":false},{"year":2016,"finding":"GCN2 (EIF2AK4) activation upon infection with adherent-invasive E. coli (AIEC) drives autophagy by promoting ATF4 binding to promoters of autophagy genes (MAP1LC3B, BECN1, SQSTM1, ATG3, ATG7). EIF2AK4 depletion inhibits autophagy, increases AIEC intracellular replication, and elevates pro-inflammatory cytokines. In vivo, eif2ak4-/- mice show increased intestinal AIEC colonization and aggravated inflammation.","method":"EIF2AK4 siRNA knockdown in intestinal epithelial cells, eif2ak4-/- mice, autophagy flux assay, ChIP for ATF4 binding to autophagy gene promoters, bacterial colony counting","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP establishing direct transcriptional mechanism, combined with in vitro and in vivo genetic loss-of-function","pmids":["26986695"],"is_preprint":false},{"year":2023,"finding":"ATP-competitive GCN2 inhibitor Gcn2iB can paradoxically activate GCN2 at low concentrations, increasing eIF2 phosphorylation and ATF4 expression. This activation occurs even in GCN2 mutants lacking functional regulatory domains or with kinase domain substitutions found in GCN2-deficient human patients, suggesting the inhibitor directly engages the kinase domain to cause activation.","method":"In vitro GCN2 kinase assay, cell-based eIF2α phosphorylation and ATF4 reporter assays, GCN2 regulatory domain deletion mutants, patient-derived GCN2 kinase domain mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro kinase assay combined with systematic mutagenesis and cell-based validation","pmids":["36898579"],"is_preprint":false},{"year":2021,"finding":"ATP-competitive kinase inhibitors including the pan-ErbB inhibitor neratinib directly bind and activate GCN2. Several FDA-approved kinase inhibitors (erlotinib, sunitinib) also bind and activate GCN2. GCN2 loss confers neratinib resistance by preventing neratinib-induced GCN2 binding and activation.","method":"Genome-wide CRISPR KO screen, direct binding assay (neratinib-GCN2 interaction), eIF2α phosphorylation assay, ISR activation assay","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide CRISPR screen combined with direct binding evidence and mechanistic validation","pmids":["34949839"],"is_preprint":false},{"year":2021,"finding":"Halofuginone (HF) activates GCN2 by inhibiting aminoacylation of tRNA-Pro, causing accumulation of uncharged tRNA. GCN2 deletion reduces cell survival to HF, while mTORC1 inhibition affords protection. In vivo, HF simultaneously activates both the GCN2-ISR pathway and mTORC1 in mouse liver; Gcn2-null mice show greater mTORC1 activation and develop liver steatosis and cell death.","method":"Gcn2-/- mice, HF treatment, eIF2α phosphorylation assay, mTORC1 signaling analysis, liver histology, pharmacological mTORC1 inhibition","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with pharmacological interventions and in vivo validation establishing mechanistic context","pmids":["34023907"],"is_preprint":false},{"year":2024,"finding":"mTOR directly phosphorylates GCN2 at Ser-230 via a labile physical interaction between GCN2 and mTOR. This mTOR-mediated phosphorylation enhances GCN2 activity under conditions of sustained mTORC1 activation during amino acid starvation, and the resulting GCN2 activation is independent of tRNA sensing. This phosphorylation promotes cell survival under prolonged amino acid starvation.","method":"Co-immunoprecipitation (GCN2-mTOR), in vitro kinase assay (mTOR phosphorylating GCN2-Ser230), phosphorylation site mutagenesis, eIF2α and ATF4 assays, cell survival assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and in vitro kinase assay with phosphosite identification, single lab, novel mechanism requiring replication","pmids":["39013537"],"is_preprint":false},{"year":2011,"finding":"A loss-of-function mutation in Eif2ak4 (GCN2) in mice increases susceptibility to mouse cytomegalovirus (MCMV) and human adenovirus (double-stranded DNA viruses). Macrophages from Eif2ak4(atc/atc) mice fail to phosphorylate eIF2α in response to MCMV infection, demonstrating that GCN2-dependent translational arrest contributes to the antiviral response to DNA viruses in vivo.","method":"ENU-induced loss-of-function mutation screen, eIF2α phosphorylation assay in macrophages, in vivo viral infection model","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function with direct biochemical readout and in vivo viral susceptibility phenotype","pmids":["22114338"],"is_preprint":false},{"year":2017,"finding":"GCN2 deficiency in PVOD leads to decreased ATF3-dependent p38 MAPK phosphorylation inhibition, resulting in enhanced transcription of collagen I genes (col1a1, col1a2) and increased collagen deposition in pulmonary arterial smooth muscle cells. This mechanism was validated in GCN2 KO cell lines and iPSC-derived smooth muscle cells from PVOD patients.","method":"CRISPR-generated GCN2 KO cell lines, iPSC differentiation from PVOD patient PBMCs, collagen I expression assay, p38 phosphorylation assay, ATF3 analysis","journal":"Journal of cardiovascular pharmacology and therapeutics","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — CRISPR KO with patient-derived iPSCs and mechanistic pathway analysis, single lab","pmids":["33988041"],"is_preprint":false},{"year":2012,"finding":"IFN-γ promotes tryptophan depletion in human kidney epithelial cells, which activates GCN2 and leads to increased autophagic flux. Tryptophan supplementation and siRNA knockdown of GCN2 inhibit IFN-γ-induced autophagy. GCN2-mediated autophagy regulates secretion of inflammatory cytokines and growth factors in response to IFN-γ.","method":"siRNA knockdown of GCN2, autophagy flux assay, tryptophan supplementation rescue, cytokine secretion measurement","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — RNA interference loss-of-function with rescue experiment, single lab, functional autophagy readout","pmids":["22896630"],"is_preprint":false},{"year":2017,"finding":"Tryptophan deprivation increases kynurenine uptake by upregulating SLC7A5 (LAT1) expression in a GCN2-dependent manner, linking GCN2 activation to enhanced kynurenine transport and downstream AHR pathway sensitization.","method":"GCN2 knockdown/inhibition, kynurenine uptake assay, SLC7A5 expression analysis, LAT1 functional transport assay","journal":"Journal for immunotherapy of cancer","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — GCN2 genetic and pharmacological inhibition with transporter expression and functional uptake assays, single lab","pmids":["37344101"],"is_preprint":false},{"year":2020,"finding":"In amygdalar PKC-δ neurons, leucine deficiency activates GCN2/ATF4 signaling to promote white adipose tissue (WAT) browning via sympathetic nervous system activation. GCN2 knockdown in amygdalar PKC-δ neurons blocks leucine deprivation-induced WAT browning, which is reversed by ATF4 overexpression.","method":"Amygdala-specific GCN2 knockdown (viral vector), PKC-δ neuronal inhibition, WAT browning markers, ATF4 overexpression rescue","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — region-specific knockdown with rescue experiment, single lab, novel neuroendocrine mechanism","pmids":["32504036"],"is_preprint":false},{"year":2017,"finding":"GCN2 is constitutively localized to the nucleolus or recruited there by amino acid starvation stress. siRNA-mediated GCN2 depletion increases small RNA transcripts (tRNA, 5S rRNA) via RNA polymerase III and activates the p53 pathway. This derepression and p53 activation are restored by co-depletion of BRF1 (an RNA pol III subunit), suggesting GCN2 negatively regulates RNA pol III activity in the nucleolus.","method":"Immunofluorescence (nucleolar localization), siRNA knockdown, small RNA quantification, p53 pathway analysis, BRF1 co-knockdown rescue","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — subcellular localization by immunofluorescence with functional knockdown and rescue, single lab","pmids":["28189689"],"is_preprint":false},{"year":2013,"finding":"GCN2 regulates hepatic gluconeogenesis through regulation of C/EBPβ expression. Gcn2-deficient mice show reduced gluconeogenic capacity and failure to induce C/EBPβ during fasting; liver-specific Cebpβ knockout mice phenocopy the reduced fasting gluconeogenesis seen in Gcn2-deficient mice, placing GCN2 upstream of C/EBPβ in this pathway.","method":"Gcn2-/- mice, pyruvate tolerance test, gluconeogenic enzyme expression, TCA cycle intermediate measurement, C/EBPβ expression analysis, liver-specific Cebpβ KO mice","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with two knockout models and metabolic phenotyping, single lab","pmids":["23900421"],"is_preprint":false},{"year":2016,"finding":"Drosophila GCN2 is required for 4E-BP transcriptional induction via ATF4; the 4E-BP intron contains ATF4-binding sites. GCN2 is required for lifespan extension in response to dietary amino acid restriction, and gcn2 mutant flies have reduced levels of stress-responsive protein synthesis as measured by metabolic labeling combined with click chemistry.","method":"GCN2 mutant Drosophila, 4E-BP reporter assays, ATF4 binding site analysis, metabolic labeling (click chemistry) for nascent protein synthesis, lifespan assays","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mutant with multiple molecular and phenotypic readouts, single organism model","pmids":["27979906"],"is_preprint":false},{"year":2022,"finding":"In nutrient-rich conditions, GCN2 supports cancer cell proliferation by stimulating 47S rRNA transcription via nuclear translocation of methionyl-tRNA synthetase (MetRS). GCN2 inhibition prevents nuclear translocation of MetRS, causing nucleolar stress, mTORC1 inhibition, and autophagy induction. Under metabolic stress, GCN2 represses 47S rRNA expression through the canonical ISR axis.","method":"GCN2 inhibition (pharmacological and genetic), MetRS nuclear/cytoplasmic fractionation, 47S rRNA quantification, mTORC1 activity assay, autophagy assay, patient-derived tumoroids","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — pharmacological and genetic inhibition with MetRS localization and functional readouts, single lab","pmids":["37452637"],"is_preprint":false},{"year":2019,"finding":"High MYC levels in APC-deficient colorectal cancer cells induce phosphorylation of eIF2α via GCN2 (and PKR), forming a negative feedback loop. Pharmacological inhibition of GCN2 phenocopies eIF2B5 depletion, causing MYC-dependent apoptosis and demonstrating therapeutic efficacy in patient-derived tumor organoids.","method":"GCN2 pharmacological inhibition, eIF2α phosphorylation assay, tumor organoid model, genetic epistasis (APC, MYC, GCN2)","journal":"Nature cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and genetic approaches in patient-derived models with defined pathway placement, single lab","pmids":["31685988"],"is_preprint":false}],"current_model":"EIF2AK4/GCN2 is a serine/threonine eIF2α kinase that senses amino acid insufficiency primarily through its HisRS-like domain binding uncharged tRNAs (and via the ribosomal P-stalk) to relieve autoinhibition involving an inhibitory pseudokinase–kinase domain interaction, whereupon active GCN2 phosphorylates eIF2α at Ser-51 (suppressing bulk translation while preferentially translating ATF4/GCN4 mRNAs), and also phosphorylates additional substrates including eIF2β, Gcn20, FBXO22 (leading to mTOR ubiquitination), and HIV-1 integrase; GCN2 activity is regulated by Hsp90 chaperone, TOR/TAP42-dependent Ser-577 phosphorylation, Gcn1/Gcn20 co-activators, the Yih1/IMPACT inhibitor competing for Gcn1 binding, and mTOR-mediated phosphorylation at Ser-230, with diverse biological roles including antiviral defense, synaptic plasticity via the ATF4/CREB axis, angiogenesis, immune cell polarization, wound healing, HSC proteostasis, and when mutated (loss-of-function biallelic mutations), pulmonary veno-occlusive disease/pulmonary capillary hemangiomatosis."},"narrative":{"mechanistic_narrative":"EIF2AK4/GCN2 is a serine/threonine eIF2α kinase that functions as the central translational sensor of amino acid insufficiency, coupling nutrient and ribosomal stress to a programmed reduction in bulk protein synthesis and preferential translation of stress mRNAs [PMID:12215525, PMID:8798780]. Catalysis requires its conserved kinase domain, and active GCN2 phosphorylates eIF2α specifically at Ser-51 through recognition determinants that include residues flanking the phospho-acceptor and a distal surface in the K79GYID83 motif [PMID:2188100, PMID:8798780, PMID:15798194]. Activation is gated by a bipartite tRNA-binding module formed by the HisRS-related domain plus a C-terminal ribosome-binding segment: uncharged tRNA binding relieves an inhibitory intramolecular interaction between the regulatory regions and the kinase, while aminoacylation weakens tRNA binding [PMID:10983975, PMID:8798780]. Crystallographic and biochemical work shows the resting kinase adopts an autoinhibited closed conformation, and that productive signaling additionally requires kinase-domain dimerization through a conserved intermolecular salt bridge, an interdigitated C-terminal dimer, and allosteric stimulation of the kinase by the pseudokinase (YKD) domain [PMID:15964839, PMID:17202131, PMID:24719324, PMID:24811037]. In mammals GCN2 is potently activated by the ribosomal P-stalk (uL10 and the P1/P2 C-terminal tails) and by ribosomal collisions, with distinct stress types—amino acid depletion versus elongation stalling—engaging uncharged-tRNA sensing or collision sensing respectively through the same HisRS-like domain [PMID:30804176, PMID:37043534, PMID:38281137]. GCN2 activity is further set by the Hsp90 chaperone, TOR-dependent Ser-577 phosphorylation, and the Gcn1/Gcn20 co-activators that are antagonized by the Yih1/IMPACT competitor [PMID:10567567, PMID:12654728, PMID:21239490], and GCN2 itself extends signaling beyond eIF2α by phosphorylating eIF2β to restrict ternary-complex recycling and by phosphorylating FBXO22 to drive K27-linked ubiquitination of mTOR at Lys-2066 and suppress mTORC1 [PMID:33743194, PMID:37979583]. Downstream, GCN2 acts largely through the ATF4 axis to control diverse processes—synaptic plasticity and memory via ATF4/CREB, tumor amino-acid adaptation and SLC transporter expression, angiogenesis via VEGF, myeloid and macrophage polarization, autophagy, wound-healing cell migration, and hematopoietic stem cell proteostasis [PMID:16121183, PMID:20473272, PMID:36107759, PMID:29570992, PMID:31836669, PMID:26986695, PMID:34597669, PMID:35803229]. GCN2 also functions in antiviral defense, restricting RNA and DNA viruses and directly phosphorylating HIV-1 integrase at Ser-255 [PMID:16601681, PMID:22114338, PMID:28536474]. Biallelic loss-of-function mutations in EIF2AK4 underlie pulmonary veno-occlusive disease, where GCN2 deficiency derepresses collagen I via loss of ATF3-dependent p38 MAPK control [PMID:33988041].","teleology":[{"year":1990,"claim":"Establishing that GCN2 is a genuine protein kinase whose catalytic activity drives GCN4 induction defined the core of the general amino acid control pathway.","evidence":"Catalytic-lysine mutagenesis abolishing autophosphorylation and in vivo GCN4-lacZ regulation, plus deletion of flanking regulatory domains, in yeast","pmids":["2188100"],"confidence":"High","gaps":["Direct physiological substrate not yet identified at this stage","Mechanism by which flanking domains lower the tRNA-activation threshold unresolved"]},{"year":1996,"claim":"Mapping eIF2α as the substrate and showing the HisRS-related domain is required for its phosphorylation linked nutrient sensing to translation initiation.","evidence":"Cell-free kinase assay on recombinant eIF2α with HisRS-domain point mutants, correlated to in vivo defects","pmids":["8798780"],"confidence":"High","gaps":["Did not establish how the HisRS domain transmits signal to the kinase","Structural basis of Ser-51 selectivity unknown"]},{"year":2000,"claim":"Defining a bipartite tRNA-binding module that intramolecularly inhibits the kinase, relieved by uncharged tRNA, explained how amino acid status is decoded.","evidence":"In vitro binding of HisRS+C-term to the kinase domain, aminoacylation-dependent tRNA binding, and activating E803V mutant analysis; parallel demonstration that mouse GCN2 phosphorylates eIF2α at Ser-51","pmids":["10983975","10655230"],"confidence":"High","gaps":["Conformational details of activation not resolved","Whether mammalian and yeast activation modes are identical not addressed"]},{"year":1991,"claim":"Demonstrating GCN2 association with 60S subunits and polysomes via its extreme C-terminus placed the kinase at the ribosome where deacylated tRNAs accumulate.","evidence":"Sucrose-gradient sedimentation, salt-dependent dissociation, and C-terminal deletion analysis in yeast","pmids":["2038314"],"confidence":"High","gaps":["Molecular contact on the ribosome not identified","Functional consequence of ribosome binding for activation not yet dissected"]},{"year":2005,"claim":"Structural and dimer-interface studies revealed the activation logic of the kinase domain: a closed autoinhibited conformation relieved by hinge remodeling and obligatory dimerization.","evidence":"Crystal structures of WT and R794G kinase domains; charge-swap mutagenesis of a conserved dimer salt bridge across GCN2/PKR/PERK with in vitro and yeast validation; eIF2α surface-residue mutagenesis defining substrate recognition","pmids":["15964839","17202131","15798194"],"confidence":"High","gaps":["Full-length activation conformation not visualized","How HisRS/tRNA binding mechanically opens the kinase not directly observed"]},{"year":2003,"claim":"Identifying TOR-driven Ser-577 phosphorylation and Hsp90 dependence showed GCN2 activity is set by upstream signaling and chaperone maturation, not tRNA alone.","evidence":"S577A mutagenesis with rapamycin/TAP42 epistasis (1999 Hsp90 work used reciprocal Co-IP, inhibitors, and ts mutants)","pmids":["12654728","10567567"],"confidence":"High","gaps":["Mammalian conservation of Ser-577 control not tested here","Kinase responsible for Ser-577 not directly identified"]},{"year":2002,"claim":"Knockout mice established GCN2 as the essential eIF2α kinase for amino acid deprivation in mammals, validating physiological relevance in vivo.","evidence":"Gcn2-/- ES cells and perfused liver failing to induce eIF2α phosphorylation under amino acid limitation, with dietary lethality phenotype","pmids":["12215525"],"confidence":"High","gaps":["Tissue-specific downstream programs not yet defined","Non-eIF2α substrates not explored"]},{"year":2006,"claim":"Showing GCN2 senses viral RNA and restricts viral replication extended its sensor role beyond nutrients into innate antiviral defense.","evidence":"In vitro activation by Sindbis genomic RNA via the HisRS domain, plus GCN2-/- cells/mice with increased viral susceptibility and kinase-dead K618R rescue failure; later ENU loss-of-function mice showed susceptibility to DNA viruses","pmids":["16601681","22114338"],"confidence":"High","gaps":["How viral RNA and tRNA inputs are distinguished by the same domain unclear","Breadth of viral ligands not mapped"]},{"year":2005,"claim":"Linking GCN2 to ATF4/CREB-dependent synaptic plasticity opened the neuronal arm of GCN2 signaling.","evidence":"Gcn2-/- mice with altered LTP, memory behavior, and reduced hippocampal ATF4","pmids":["16121183"],"confidence":"High","gaps":["Local translational targets in neurons not enumerated","Activating stimulus in resting neurons not defined"]},{"year":2014,"claim":"Dissecting C-terminal dimerization and pseudokinase-kinase allostery revealed the intramolecular architecture coupling sensing domains to catalysis.","evidence":"Crystal structures of murine/yeast CTD dimers with disruption mutants, and YKD αE/αI mutagenesis modulating YKD-KD interaction and GCN4 reporter output","pmids":["24719324","24811037"],"confidence":"High","gaps":["Mammalian CTD does not stably bind ribosomes, leaving its in vivo role open","Order of dimerization and tRNA-binding events not resolved"]},{"year":2019,"claim":"Identifying the ribosomal P-stalk as the principal mammalian activator and distinguishing collision- versus tRNA-driven activation reframed GCN2 as a ribosome-state sensor.","evidence":"In vitro reconstitution with purified P-stalk and HDX-MS (human); yeast genetic epistasis separating tethered-P-stalk from uncharged-tRNA activation; later domain/collision analysis across stresses","pmids":["30804176","37043534","38281137"],"confidence":"High","gaps":["Quantitative contribution of each input in cells under physiological stress not settled","How P-stalk and tRNA signals converge structurally on the kinase unclear"]},{"year":2017,"claim":"Defining Gcn1/Gcn20 co-activation and Yih1/IMPACT competition for Gcn1 established the activator/inhibitor checkpoint controlling GCN2 at ribosomes.","evidence":"RWD-domain mutagenesis and reciprocal binding assays (Yih1/IMPACT, 2011) and S. pombe tRNA-site and Gcn1-deletion epistasis across multiple stresses","pmids":["21239490","28771613"],"confidence":"Medium","gaps":["Stoichiometry of the Gcn1/Gcn20/GCN2 complex on the ribosome not defined","Cross-stress findings rely on genetic, not reconstituted, evidence"]},{"year":2021,"claim":"Discovery of non-eIF2α substrates (eIF2β, Gcn20, FBXO22, HIV-1 integrase) broadened GCN2's output to direct control of ternary-complex recycling, feedback, mTORC1, and viral targets.","evidence":"Phosphoproteomics with eIF2β-eIF5 and Gcn20 feedback validation; in vitro kinase/ubiquitination reconstitution for FBXO22→mTOR K2066; in vitro kinase mapping of HIV-1 integrase Ser-255 with infectivity assays","pmids":["33743194","37979583","28536474"],"confidence":"High","gaps":["Full substrate repertoire in mammalian cells not catalogued","Relative physiological weighting of eIF2α versus alternative substrates unknown"]},{"year":2023,"claim":"Mapping diverse downstream physiology placed GCN2/ATF4 upstream of amino-acid transport, angiogenesis, immune polarization, autophagy, migration, and stem-cell proteostasis.","evidence":"Genetic and pharmacological loss-of-function with in vivo models across tumors (SLC/transporters, MYC feedback), endothelium (VEGF), myeloid cells, intestinal autophagy (ATF4 ChIP), keratinocyte migration, and HSCs","pmids":["29570992","31836669","26986695","26986695","34597669","35803229","36107759","20473272"],"confidence":"High","gaps":["Whether these effects are all ATF4-dependent or involve alternative substrates not uniformly resolved","Tissue-specific activating signals not always defined"]},{"year":2024,"claim":"Defining bidirectional GCN2-mTOR crosstalk and paradoxical inhibitor-induced activation refined the pharmacology and regulatory wiring of the kinase.","evidence":"mTOR→GCN2 Ser-230 phosphorylation (Co-IP, in vitro kinase); ATP-competitive inhibitors (Gcn2iB, neratinib) that bind and activate GCN2, validated in patient-derived kinase-domain mutants and CRISPR screens","pmids":["39013537","36898579","34949839"],"confidence":"Medium","gaps":["Ser-230 phosphorylation is single-lab and awaits independent confirmation","Structural basis of inhibitor-induced activation not solved"]},{"year":2017,"claim":"Patient-derived models tied biallelic EIF2AK4 loss to pulmonary veno-occlusive disease through derepressed collagen I.","evidence":"CRISPR GCN2 KO lines and PVOD patient iPSC-derived smooth muscle cells showing ATF3/p38-dependent collagen I upregulation","pmids":["33988041"],"confidence":"Medium","gaps":["Single-lab mechanism not independently replicated","Causal chain from eIF2α/ATF4 to ATF3/p38 incompletely defined"]},{"year":null,"claim":"How the multiple activating inputs (uncharged tRNA, P-stalk/collisions, viral RNA, mTOR phosphorylation, kinase-directed inhibitors) are integrated into a single quantitative output, and how non-eIF2α substrate phosphorylation is prioritized in vivo, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified structural model of full-length activated GCN2 on the ribosome","Relative in vivo contribution of eIF2α versus eIF2β/FBXO22 substrates unknown","Mammalian conservation of several yeast-defined regulatory phosphosites not fully established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,2,4,7,17,22,24]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1,2,24]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,12]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005840","term_label":"ribosome","supporting_discovery_ids":[3,10,19]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[41]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,11,17]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[17]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[11,14,20]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[31,38]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[25,29]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[37]}],"complexes":[],"partners":["EIF2S1","HSP90","GCN1","GCN20","FBXO22","MTOR","IMPACT"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9P2K8","full_name":"eIF-2-alpha kinase GCN2","aliases":["Eukaryotic translation initiation factor 2-alpha kinase 4","GCN2-like protein"],"length_aa":1649,"mass_kda":186.9,"function":"Metabolic-stress sensing protein kinase that phosphorylates the alpha subunit of eukaryotic translation initiation factor 2 (EIF2S1/eIF-2-alpha) in response to low amino acid availability (PubMed:25329545, PubMed:32610081). Plays a role as an activator of the integrated stress response (ISR) required for adaptation to amino acid starvation (By similarity). EIF2S1/eIF-2-alpha phosphorylation in response to stress converts EIF2S1/eIF-2-alpha into a global protein synthesis inhibitor, leading to a global attenuation of cap-dependent translation, and thus to a reduced overall utilization of amino acids, while concomitantly initiating the preferential translation of ISR-specific mRNAs, such as the transcriptional activator ATF4, and hence allowing ATF4-mediated reprogramming of amino acid biosynthetic gene expression to alleviate nutrient depletion (PubMed:32610081). Binds uncharged tRNAs (By similarity). Required for the translational induction of protein kinase PRKCH following amino acid starvation (By similarity). Involved in cell cycle arrest by promoting cyclin D1 mRNA translation repression after the unfolded protein response pathway (UPR) activation or cell cycle inhibitor CDKN1A/p21 mRNA translation activation in response to amino acid deprivation (PubMed:26102367). Plays a role in the consolidation of synaptic plasticity, learning as well as formation of long-term memory (By similarity). Plays a role in neurite outgrowth inhibition (By similarity). Plays a proapoptotic role in response to glucose deprivation (By similarity). Promotes global cellular protein synthesis repression in response to UV irradiation independently of the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) and p38 MAPK signaling pathways (By similarity). Plays a role in the antiviral response against alphavirus infection; impairs early viral mRNA translation of the incoming genomic virus RNA, thus preventing alphavirus replication (By similarity) (Microbial infection) Plays a role in modulating the adaptive immune response to yellow fever virus infection; promotes dendritic cells to initiate autophagy and antigene presentation to both CD4(+) and CD8(+) T-cells under amino acid starvation (PubMed:24310610)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9P2K8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/EIF2AK4","classification":"Not Classified","n_dependent_lines":127,"n_total_lines":1208,"dependency_fraction":0.10513245033112582},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/EIF2AK4","total_profiled":1310},"omim":[{"mim_id":"615319","title":"IMPACT RWD DOMAIN PROTEIN; IMPACT","url":"https://www.omim.org/entry/615319"},{"mim_id":"609280","title":"EUKARYOTIC TRANSLATION INITIATION FACTOR 2-ALPHA KINASE 4; EIF2AK4","url":"https://www.omim.org/entry/609280"},{"mim_id":"605614","title":"GCN1 ACTIVATOR OF EIF2AK4; GCN1","url":"https://www.omim.org/entry/605614"},{"mim_id":"605180","title":"SOLUTE CARRIER FAMILY 38 (AMINO ACID TRANSPORTER), MEMBER 2; SLC38A2","url":"https://www.omim.org/entry/605180"},{"mim_id":"265450","title":"PULMONARY VENOOCCLUSIVE DISEASE 1, AUTOSOMAL DOMINANT; PVOD1","url":"https://www.omim.org/entry/265450"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/EIF2AK4"},"hgnc":{"alias_symbol":["GCN2","KIAA1338"],"prev_symbol":[]},"alphafold":{"accession":"Q9P2K8","domains":[{"cath_id":"3.10.110.10","chopping":"20-142","consensus_level":"high","plddt":85.4172,"start":20,"end":142},{"cath_id":"1.10.510.10","chopping":"267-468","consensus_level":"high","plddt":80.7884,"start":267,"end":468},{"cath_id":"3.30.930.10","chopping":"1062-1216_1264-1387","consensus_level":"medium","plddt":87.7656,"start":1062,"end":1387},{"cath_id":"3.40.50.800","chopping":"1400-1498","consensus_level":"high","plddt":82.3629,"start":1400,"end":1498},{"cath_id":"1.20.5","chopping":"143-187","consensus_level":"medium","plddt":75.4013,"start":143,"end":187}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9P2K8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9P2K8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9P2K8-F1-predicted_aligned_error_v6.png","plddt_mean":72.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EIF2AK4","jax_strain_url":"https://www.jax.org/strain/search?query=EIF2AK4"},"sequence":{"accession":"Q9P2K8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9P2K8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9P2K8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9P2K8"}},"corpus_meta":[{"pmid":"20473272","id":"PMC_20473272","title":"The 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Aminoacylation of tRNA weakens its interaction with GCN2, and an activating mutation (E803V) that weakens PK-C-term association greatly enhanced tRNA binding.\",\n      \"method\": \"In vitro binding assays, tRNA binding assays with aminoacylated vs. deacylated tRNAs, activating mutant analysis, domain dissection\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified domains, mutagenesis, and multiple orthogonal binding assays in a focused mechanistic study\",\n      \"pmids\": [\"10983975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"GCN2 acts as a protein kinase to stimulate GCN4 expression; substitution of the conserved lysine in the kinase domain abolished both GCN2 regulatory function in vivo and autophosphorylation in vitro. The HisRS-related sequences and C-terminal segment flanking the kinase domain are positive-acting regulatory domains required for physiological substrate recognition or lowering the threshold for uncharged tRNA activation.\",\n      \"method\": \"In vitro autophosphorylation assay, in vivo reporter (GCN4-lacZ), site-directed mutagenesis, deletion analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — catalytic dead mutant abolishes both in vitro kinase activity and in vivo function; replicated across multiple domain mutations\",\n      \"pmids\": [\"2188100\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The HisRS-related sequences of GCN2 are required for phosphorylation of eIF-2α in vitro; mutations in this domain that block the general amino acid control pathway in vivo also greatly reduce eIF-2α phosphorylation in a cell-free assay using recombinant eIF-2α substrate (phosphorylation requires Ser-51 of eIF-2α).\",\n      \"method\": \"In vitro kinase assay with purified recombinant eIF-2α substrate, HisRS-domain point mutations\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro kinase assay with mutagenesis, correlated with in vivo phenotype\",\n      \"pmids\": [\"8798780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"GCN2 physically associates with 60S ribosomal subunits and polysomes in yeast cell extracts; it can be dissociated from 60S subunits by 0.5 M KCl. The extreme C-terminal segment of GCN2 is essential for ribosome interaction, and this segment is also required for GCN4 translational activation in vivo.\",\n      \"method\": \"Sucrose gradient sedimentation, nondenaturing gel electrophoresis, ribosome dissociation experiments, C-terminal deletion analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct fractionation experiments with functional validation by deletion mutagenesis; replicated across multiple conditions\",\n      \"pmids\": [\"2038314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Mouse GCN2, a mammalian homologue of yeast GCN2, phosphorylates recombinant eIF-2α in vitro requiring the kinase catalytic domain and HisRS-related sequences, and the phosphorylation requires Ser-51 of eIF-2α. Three mouse GCN2 isoforms are encoded by a single gene with differential N-terminal sequences.\",\n      \"method\": \"In vitro kinase assay with recombinant eIF-2α, expression of mGCN2 in yeast, Ser-51 mutagenesis\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with Ser-51 mutagenesis and complementary in vivo yeast system\",\n      \"pmids\": [\"10655230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structures of the GCN2 protein kinase domain (wild-type and R794G mutant) reveal that autoinhibition results from stabilization of a closed conformation that restricts ATP binding. The R794G mutation increases hinge-region flexibility between N- and C-lobes, enhancing ATP binding and hydrolysis, and provides a model for how tRNA binding to the HisRS domain remodels the hinge for kinase activation.\",\n      \"method\": \"X-ray crystallography of apo and ATP/AMPPNP-bound kinase domain; biochemical validation of R794G activating mutant\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures of both wild-type and activating mutant with functional correlation\",\n      \"pmids\": [\"15964839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The TOR pathway negatively regulates GCN2 in yeast by promoting phosphorylation of Ser-577 in GCN2, which reduces tRNA binding activity and inhibits kinase function. Rapamycin-induced TOR inhibition leads to Ser-577 dephosphorylation via TAP42-regulated type 2A-related phosphatases, thereby activating GCN2 and increasing eIF2α phosphorylation and GCN4 translation.\",\n      \"method\": \"Phosphorylation-site mutagenesis (S577A), rapamycin treatment, GCN4-lacZ reporter, eIF2α phosphorylation assays, TAP42 genetic analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — site-directed mutagenesis combined with pharmacological and genetic epistasis across multiple readouts\",\n      \"pmids\": [\"12654728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GCN2 and PKR phosphorylate eIF2α on Ser-51; residues flanking Ser-51 (Glu-49) and a remote surface residue Asp-83 in the K79GYID83 motif are critical for kinase-substrate recognition. Ala substitution of Asp-83 eliminates phosphorylation by both GCN2 and PKR in vivo and in vitro, establishing that distal surface residues contribute to substrate recognition. Separately, mutations that block translational regulation but not Ser-51 phosphorylation impair eIF2B binding to phospho-eIF2α.\",\n      \"method\": \"In vivo and in vitro phosphorylation assays, eIF2α mutagenesis, eIF2B binding assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with systematic mutagenesis correlated with in vivo function\",\n      \"pmids\": [\"15798194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"A conserved intermolecular salt bridge between an Arg and Asp/Glu residue (equivalent to Arg-262/Asp-266 in PKR) at the kinase domain dimer interface is essential for GCN2 (and PKR, PERK) activity. Single charge-reversal mutations in either residue abolish kinase function in yeast cells and in vitro; double mutations restoring salt bridge with opposite polarity restore function, demonstrating that dimerization via this interface is required for eIF2α kinase activation.\",\n      \"method\": \"Site-directed mutagenesis, in vivo yeast functional assay, in vitro kinase assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — charge-swap mutagenesis with both in vitro and in vivo validation across three eIF2α kinases\",\n      \"pmids\": [\"17202131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"GCN2 forms a complex with the molecular chaperone Hsp90 both in vitro and in vivo in yeast. Hsp90 inhibitors (geldanamycin, macbecin I) enhance GCN2-Hsp90 association and inhibit GCN2 kinase activity in vitro; in vivo, macbecin I strongly reduces GCN2 protein levels. Hsp90 cochaperones Cdc37, Sti1, and Sba1 are required for the amino acid starvation response, indicating Hsp90 is required for GCN2 maturation and regulation.\",\n      \"method\": \"Co-immunoprecipitation in vitro and in vivo, Hsp90 inhibitor treatment, temperature-sensitive Hsp90 mutant analysis, GCN4-lacZ reporter\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP in vitro and in vivo combined with pharmacological and genetic validation\",\n      \"pmids\": [\"10567567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Human GCN2 is potently stimulated by ribosomes and, to a lesser extent, by uncharged tRNA in a reconstituted in vitro system. The ribosomal P-stalk domain II of uL10 is the principal binding site for GCN2; the conserved 14-residue C-terminal tails of P1/P2 P-stalk proteins are also essential for GCN2 activation. HDX-MS showed conformational changes in both the HisRS-like and kinase domains of GCN2 upon P-stalk binding.\",\n      \"method\": \"In vitro reconstitution with purified components, HDX-MS, recombinant P-stalk complex binding assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified recombinant human GCN2 and P-stalk components, HDX-MS structural data, multiple orthogonal methods\",\n      \"pmids\": [\"30804176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"GCN2 is essential for eIF2α phosphorylation in response to amino acid deprivation in mammals. Gcn2-/- mice fail to induce eIF2α phosphorylation in leucine-deprived embryonic stem cells, and perfused livers from Gcn2-/- mice fail to show increased eIF2α phosphorylation or decreased eIF2B activity upon histidine limitation. Loss of GCN2 increases prenatal/neonatal mortality when mothers are fed amino acid-deficient diets.\",\n      \"method\": \"Gcn2 knockout mouse, eIF2α phosphorylation assay in ES cells and perfused liver, eIF2B activity assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with direct biochemical readout of substrate phosphorylation in multiple tissue systems\",\n      \"pmids\": [\"12215525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Mammalian GCN2 is specifically activated in vitro by binding of two nonadjacent regions of Sindbis virus genomic RNA to its HisRS-related domain. Endogenous GCN2 is activated during Sindbis virus infection in cells. GCN2-/- mouse fibroblasts show increased permissiveness to Sindbis virus and VSV infection, and GCN2-/- mice are highly susceptible to intranasal SV infection with higher brain virus titers. Catalytically inactive GCN2-K618R fails to impair viral replication, and GCN2 inhibits SV replication by blocking early viral translation.\",\n      \"method\": \"In vitro RNA-binding and kinase activation assay, GCN2 knockout fibroblasts and mice, viral infection assays, kinase-dead mutant (K618R)\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro activation assay combined with genetic knockout in cells and in vivo, plus catalytic-dead mutant validation\",\n      \"pmids\": [\"16601681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GCN2 regulates hippocampal synaptic plasticity and memory through modulation of ATF4/CREB pathway. In GCN2-/- mice, ATF4 expression is reduced and CREB activity is increased in the hippocampus, consistent with GCN2-activated eIF2α phosphorylation normally promoting ATF4 mRNA translation which antagonizes CREB.\",\n      \"method\": \"GCN2 knockout mouse, electrophysiology (LTP), behavioral testing (Morris water maze), ATF4 and CREB activity measurements\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with multiple orthogonal readouts (electrophysiology, behavior, molecular signaling) in a high-profile study\",\n      \"pmids\": [\"16121183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Both amino acid and glucose deprivation activate GCN2 to upregulate ATF4 target genes involved in amino acid synthesis and transport in tumour cells. GCN2 activation and increased phospho-eIF2α are observed in human and mouse tumours; abrogation of GCN2 or ATF4 expression significantly inhibits tumour growth in vivo.\",\n      \"method\": \"GCN2 knockdown/overexpression, eIF2α phosphorylation assay, in vivo tumour growth experiments, ATF4 target gene expression analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function (knockdown) combined with in vivo tumour models and molecular pathway analysis\",\n      \"pmids\": [\"20473272\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal structures of murine and yeast GCN2 C-terminal domains (CTDs) reveal an unusual interdigitated dimeric form; disruption of the dimeric form of murine CTD eliminates GCN2 translational control function. Despite shared core structure, murine GCN2 CTD does not stably associate with ribosomes whereas yeast GCN2 CTD does, indicating regulatory differences between yeast and mammalian GCN2.\",\n      \"method\": \"X-ray crystallography, dimerization-disrupting mutations with functional assays, ribosome association assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures of both yeast and murine CTDs combined with functional validation of dimerization mutants\",\n      \"pmids\": [\"24719324\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The GCN2 pseudokinase domain (YKD) directly interacts with the kinase domain (KD) to allosterically stimulate kinase activity in amino acid-starved cells. Substitutions in predicted helices αE and αI of the YKD impair GCN2 activation without reducing uncharged tRNA binding; αI substitutions identified as Gcd- (constitutively active) enhance YKD-KD interactions in vitro, while αE/αI Gcn- substitutions suppress this effect.\",\n      \"method\": \"Mutational analysis of YKD, in vitro YKD-KD interaction assay, in vivo GCN4-lacZ reporter, tRNA binding assays\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro domain interaction assay combined with systematic mutagenesis and in vivo functional readout\",\n      \"pmids\": [\"24811037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Gcn2 phosphorylates the β-subunit of eIF2 to promote its association with eIF5, preventing spontaneous nucleotide exchange on eIF2 and restricting recycling of the initiator Met-tRNA-bound eIF2-GDP ternary complex in amino-acid-starved cells—a mechanism parallel to eIF2α phosphorylation-dependent eIF2B sequestration. Gcn2 also phosphorylates Gcn20 to antagonize formation of the Gcn2-stimulatory Gcn1-Gcn20 complex in a negative feedback loop.\",\n      \"method\": \"Quantitative phosphoproteomics, Co-immunoprecipitation, translation initiation assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — quantitative phosphoproteomics identifying novel substrates with biochemical validation of eIF2β-eIF5 interaction and Gcn20 feedback\",\n      \"pmids\": [\"33743194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Yih1 (yeast) / IMPACT (mammalian) inhibits GCN2 by competing with GCN2 for binding to the GCN2 activator Gcn1 via its RWD domain. Gcn1 binding and GCN2 inhibition require residues Asp-102 and Glu-106 in helix 3 of the RWD domain. Yih1 also binds G-actin independently of Gcn1 binding, but actin binding is dispensable for GCN2 inhibition.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding assays, site-directed mutagenesis of Yih1 RWD domain, in vivo GCN4-lacZ reporter\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding assays combined with mutagenesis and in vivo functional validation\",\n      \"pmids\": [\"21239490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In yeast, GCN2 activation by ribosome stalling (starvation-independent conditions) requires at least one P1/P2 P-stalk heterodimer tethered to uL10 of the ribosomal P-stalk, the tRNA- and ribosome-binding domains of Gcn2, and the positive effectors Gcn1/Gcn20. By contrast, amino acid starvation-induced GCN2 activation does not require tethered P1/P2 proteins, suggesting that uncharged tRNAs can substitute for the P-stalk in activating GCN2 at ribosomes with empty A-sites.\",\n      \"method\": \"Genetic analysis in yeast (P-stalk deletion mutants, GCN2 domain mutants, epistasis), eIF2α phosphorylation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic genetic epistasis with multiple independent stalling conditions distinguishing two activation mechanisms\",\n      \"pmids\": [\"37043534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Multiple mechanisms activate GCN2 depending on stress type: ribosomal collisions are essential for GCN2 activation by translational elongation inhibitors (stalling conditions), while direct association of GCN2 with uncharged tRNAs is the primary mechanism when amino acid depletion causes tRNA deacylation. Both mechanisms require the HisRS-like regulatory domain of GCN2. UV irradiation activates GCN2 via decreased amino acids and increased uncharged tRNAs rather than ribosome collisions.\",\n      \"method\": \"Domain mutagenesis, ribosome collision assays, tRNA deacylation assays, selective inhibitor treatment, eIF2α phosphorylation assays under multiple stress conditions\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic analysis distinguishing multiple mechanisms across diverse stress conditions with domain mutants\",\n      \"pmids\": [\"38281137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Mutation of tRNA-binding site on GCN2 or deletion of Gcn1 abolishes GCN2 activation under all investigated stress conditions (amino acid starvation, UV irradiation, and oxidative stress) in fission yeast, indicating that tRNA binding to GCN2 is required for activation not only by starvation but also by other stresses.\",\n      \"method\": \"GCN2 tRNA-binding site mutagenesis, Gcn1 deletion, eIF2α phosphorylation assays under multiple stress conditions in S. pombe\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function analysis across multiple stresses, single lab with orthogonal stress conditions but no in vitro reconstitution\",\n      \"pmids\": [\"28771613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GCN2 activation upon HIV-1 infection requires GCN2's interaction with HIV-1 integrase. GCN2 phosphorylates HIV-1 integrase in vitro at Ser-255 in the C-terminal domain, and the integrase active site is required for GCN2 to target this residue. HIV-1 lentiviral particles with S255 mutation (preventing phosphorylation) show increased infectivity and viral DNA integration; MLV infectivity is also higher in GCN2 knockout cells.\",\n      \"method\": \"In vitro kinase assay with HIV-1 integrase substrate, phosphorylation site mapping (mass spectrometry), site-directed mutagenesis (S255), GCN2 Co-IP with integrase, viral infectivity assays in GCN2 KO cells\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro kinase assay identifying novel substrate with mutagenesis of phosphorylation site and functional validation in cells\",\n      \"pmids\": [\"28536474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Amino acid restriction triggers angiogenesis via the GCN2/ATF4 pathway, independently of hypoxia or HIF1α. Sulfur amino acid restriction promotes VEGF expression, EC migration and sprouting via GCN2/ATF4 signaling in vitro and increased capillary density in mouse skeletal muscle in vivo.\",\n      \"method\": \"GCN2 knockout/knockdown experiments, endothelial cell migration and sprouting assays, in vivo capillary density measurement, VEGF expression analysis, ATF4 pathway analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function with multiple cellular and in vivo readouts establishing GCN2 as upstream regulator of VEGF/angiogenesis\",\n      \"pmids\": [\"29570992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GCN2 phosphorylates FBXO22 in response to accumulation of uncharged tRNAs caused by amino acid depletion; phosphorylated FBXO22 translocates to the cytoplasm and ubiquitinates mTOR at Lys-2066 in a K27-linked manner, inhibiting mTORC1 kinase activity by preventing substrate recruitment. Mutation of mTOR Lys-2066 abolishes this regulation, rendering mTOR insensitive to amino acid starvation.\",\n      \"method\": \"In vitro kinase assay (GCN2→FBXO22 phosphorylation), ubiquitination assay, mTOR K2066 mutagenesis, cellular fractionation, mTORC1 substrate recruitment assay\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro kinase and ubiquitination reconstitution combined with mutagenesis of the target site and in vivo validation\",\n      \"pmids\": [\"37979583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GCN2 (EIF2AK4) drives ATF4-dependent maturation and polarization of macrophages and MDSCs; myeloid-lineage deletion of GCN2 shifts macrophage/MDSC phenotype toward pro-inflammatory activation and promotes antitumor immunity in melanoma. ATF4 translation is a key downstream mediator of this effect.\",\n      \"method\": \"Myeloid-specific GCN2 conditional knockout, CyTOF mass cytometry, single-cell RNA-seq, ATF4 siRNA knockdown, transcription factor binding analysis\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with multiple orthogonal readouts (CyTOF, scRNA-seq, siRNA) establishing mechanistic pathway\",\n      \"pmids\": [\"31836669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GCN2 directs keratinocyte collective cell migration during wound healing by maintaining intracellular free amino acids (particularly cysteine) and coordinating RAC1-GTP-driven reactive oxygen species generation, lamellipodia formation, and focal adhesion dynamics. GCN2 deletion or pharmacological inhibition significantly delays collective cell migration and wound closure in vitro and in vivo.\",\n      \"method\": \"GCN2 knockout cells and mice, pharmacological inhibition, wound scratch assay, RAC1-GTP pulldown, ROS measurement, transcriptomics, focal adhesion imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic and pharmacological loss-of-function with multiple mechanistic readouts and in vivo validation\",\n      \"pmids\": [\"34597669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GCN2 regulates expression of over 60 solute carrier (SLC) transporter genes including amino acid transporters; loss of GCN2 reduces amino acid import and levels in prostate cancer cells. Addition of essential amino acids or expression of SLC3A2 (4F2 heavy chain) partially restores growth following GCN2 loss, placing GCN2 upstream of SLC transporter expression for amino acid homeostasis.\",\n      \"method\": \"GCN2 knockout in prostate cancer cells, RNA-seq, CRISPR phenotypic screen, amino acid measurement, rescue experiments with amino acid supplementation and SLC3A2 overexpression, in vivo mouse models\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR KO with RNA-seq, CRISPR screen, metabolite measurements, and rescue experiments in vitro and in vivo\",\n      \"pmids\": [\"36107759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GCN2 maintains proteostasis in hematopoietic stem cells (HSCs) by sensing amino acid levels and inhibiting protein synthesis via the eIF2α axis; GCN2 also inhibits Src-mediated AKT activation to repress mitochondrial OXPHOS. GCN2 deletion impairs HSC repopulation and regeneration capacity.\",\n      \"method\": \"GCN2 knockout mice, HSC functional assays (repopulation, transplantation), protein synthesis measurement, Src/AKT phosphorylation analysis\",\n      \"journal\": \"Cell stem cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple mechanistic readouts (proteostasis, signaling pathway, function) in primary cells\",\n      \"pmids\": [\"35803229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GCN2 promotes macrophage inflammatory cytokine production (IL-6, IL-12) in response to LPS under amino acid-deficient conditions; GCN2 knockout macrophages show significantly reduced cytokine gene expression after LPS stimulation. Monocytic-lineage GCN2 knockout mice show reduced inflammatory responses and significantly decreased mortality in a lethal LPS septicemia model.\",\n      \"method\": \"GCN2 knockout macrophages and monocyte-specific conditional knockout mice, LPS challenge, cytokine measurement, in vivo septicemia model\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO at cell and whole-animal level with defined molecular and survival phenotypes\",\n      \"pmids\": [\"24248597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GCN2 interacts with NRF2 and decreases NRF2 expression in a KEAP1-dependent manner. Activation of GCN2 by halofuginone or leucine deprivation decreases NRF2 expression in hepatocytes by increasing GSK-3β activity. This defines a GCN2→GSK-3β→KEAP1→NRF2 regulatory axis in oxidative stress response.\",\n      \"method\": \"Co-immunoprecipitation (GCN2-NRF2), GCN2 knockdown (AAV8-shGcn2), pharmacological GCN2 activation and inhibition, GSK-3β activity assay, NRF2 expression analysis, in vivo hepatic steatosis models\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP plus pharmacological and in vivo genetic approaches, single lab, mechanistic follow-up incomplete\",\n      \"pmids\": [\"34954499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GCN2 (EIF2AK4) activation upon infection with adherent-invasive E. coli (AIEC) drives autophagy by promoting ATF4 binding to promoters of autophagy genes (MAP1LC3B, BECN1, SQSTM1, ATG3, ATG7). EIF2AK4 depletion inhibits autophagy, increases AIEC intracellular replication, and elevates pro-inflammatory cytokines. In vivo, eif2ak4-/- mice show increased intestinal AIEC colonization and aggravated inflammation.\",\n      \"method\": \"EIF2AK4 siRNA knockdown in intestinal epithelial cells, eif2ak4-/- mice, autophagy flux assay, ChIP for ATF4 binding to autophagy gene promoters, bacterial colony counting\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP establishing direct transcriptional mechanism, combined with in vitro and in vivo genetic loss-of-function\",\n      \"pmids\": [\"26986695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ATP-competitive GCN2 inhibitor Gcn2iB can paradoxically activate GCN2 at low concentrations, increasing eIF2 phosphorylation and ATF4 expression. This activation occurs even in GCN2 mutants lacking functional regulatory domains or with kinase domain substitutions found in GCN2-deficient human patients, suggesting the inhibitor directly engages the kinase domain to cause activation.\",\n      \"method\": \"In vitro GCN2 kinase assay, cell-based eIF2α phosphorylation and ATF4 reporter assays, GCN2 regulatory domain deletion mutants, patient-derived GCN2 kinase domain mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro kinase assay combined with systematic mutagenesis and cell-based validation\",\n      \"pmids\": [\"36898579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ATP-competitive kinase inhibitors including the pan-ErbB inhibitor neratinib directly bind and activate GCN2. Several FDA-approved kinase inhibitors (erlotinib, sunitinib) also bind and activate GCN2. GCN2 loss confers neratinib resistance by preventing neratinib-induced GCN2 binding and activation.\",\n      \"method\": \"Genome-wide CRISPR KO screen, direct binding assay (neratinib-GCN2 interaction), eIF2α phosphorylation assay, ISR activation assay\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide CRISPR screen combined with direct binding evidence and mechanistic validation\",\n      \"pmids\": [\"34949839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Halofuginone (HF) activates GCN2 by inhibiting aminoacylation of tRNA-Pro, causing accumulation of uncharged tRNA. GCN2 deletion reduces cell survival to HF, while mTORC1 inhibition affords protection. In vivo, HF simultaneously activates both the GCN2-ISR pathway and mTORC1 in mouse liver; Gcn2-null mice show greater mTORC1 activation and develop liver steatosis and cell death.\",\n      \"method\": \"Gcn2-/- mice, HF treatment, eIF2α phosphorylation assay, mTORC1 signaling analysis, liver histology, pharmacological mTORC1 inhibition\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with pharmacological interventions and in vivo validation establishing mechanistic context\",\n      \"pmids\": [\"34023907\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"mTOR directly phosphorylates GCN2 at Ser-230 via a labile physical interaction between GCN2 and mTOR. This mTOR-mediated phosphorylation enhances GCN2 activity under conditions of sustained mTORC1 activation during amino acid starvation, and the resulting GCN2 activation is independent of tRNA sensing. This phosphorylation promotes cell survival under prolonged amino acid starvation.\",\n      \"method\": \"Co-immunoprecipitation (GCN2-mTOR), in vitro kinase assay (mTOR phosphorylating GCN2-Ser230), phosphorylation site mutagenesis, eIF2α and ATF4 assays, cell survival assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and in vitro kinase assay with phosphosite identification, single lab, novel mechanism requiring replication\",\n      \"pmids\": [\"39013537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A loss-of-function mutation in Eif2ak4 (GCN2) in mice increases susceptibility to mouse cytomegalovirus (MCMV) and human adenovirus (double-stranded DNA viruses). Macrophages from Eif2ak4(atc/atc) mice fail to phosphorylate eIF2α in response to MCMV infection, demonstrating that GCN2-dependent translational arrest contributes to the antiviral response to DNA viruses in vivo.\",\n      \"method\": \"ENU-induced loss-of-function mutation screen, eIF2α phosphorylation assay in macrophages, in vivo viral infection model\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function with direct biochemical readout and in vivo viral susceptibility phenotype\",\n      \"pmids\": [\"22114338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GCN2 deficiency in PVOD leads to decreased ATF3-dependent p38 MAPK phosphorylation inhibition, resulting in enhanced transcription of collagen I genes (col1a1, col1a2) and increased collagen deposition in pulmonary arterial smooth muscle cells. This mechanism was validated in GCN2 KO cell lines and iPSC-derived smooth muscle cells from PVOD patients.\",\n      \"method\": \"CRISPR-generated GCN2 KO cell lines, iPSC differentiation from PVOD patient PBMCs, collagen I expression assay, p38 phosphorylation assay, ATF3 analysis\",\n      \"journal\": \"Journal of cardiovascular pharmacology and therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — CRISPR KO with patient-derived iPSCs and mechanistic pathway analysis, single lab\",\n      \"pmids\": [\"33988041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"IFN-γ promotes tryptophan depletion in human kidney epithelial cells, which activates GCN2 and leads to increased autophagic flux. Tryptophan supplementation and siRNA knockdown of GCN2 inhibit IFN-γ-induced autophagy. GCN2-mediated autophagy regulates secretion of inflammatory cytokines and growth factors in response to IFN-γ.\",\n      \"method\": \"siRNA knockdown of GCN2, autophagy flux assay, tryptophan supplementation rescue, cytokine secretion measurement\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — RNA interference loss-of-function with rescue experiment, single lab, functional autophagy readout\",\n      \"pmids\": [\"22896630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Tryptophan deprivation increases kynurenine uptake by upregulating SLC7A5 (LAT1) expression in a GCN2-dependent manner, linking GCN2 activation to enhanced kynurenine transport and downstream AHR pathway sensitization.\",\n      \"method\": \"GCN2 knockdown/inhibition, kynurenine uptake assay, SLC7A5 expression analysis, LAT1 functional transport assay\",\n      \"journal\": \"Journal for immunotherapy of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — GCN2 genetic and pharmacological inhibition with transporter expression and functional uptake assays, single lab\",\n      \"pmids\": [\"37344101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In amygdalar PKC-δ neurons, leucine deficiency activates GCN2/ATF4 signaling to promote white adipose tissue (WAT) browning via sympathetic nervous system activation. GCN2 knockdown in amygdalar PKC-δ neurons blocks leucine deprivation-induced WAT browning, which is reversed by ATF4 overexpression.\",\n      \"method\": \"Amygdala-specific GCN2 knockdown (viral vector), PKC-δ neuronal inhibition, WAT browning markers, ATF4 overexpression rescue\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — region-specific knockdown with rescue experiment, single lab, novel neuroendocrine mechanism\",\n      \"pmids\": [\"32504036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GCN2 is constitutively localized to the nucleolus or recruited there by amino acid starvation stress. siRNA-mediated GCN2 depletion increases small RNA transcripts (tRNA, 5S rRNA) via RNA polymerase III and activates the p53 pathway. This derepression and p53 activation are restored by co-depletion of BRF1 (an RNA pol III subunit), suggesting GCN2 negatively regulates RNA pol III activity in the nucleolus.\",\n      \"method\": \"Immunofluorescence (nucleolar localization), siRNA knockdown, small RNA quantification, p53 pathway analysis, BRF1 co-knockdown rescue\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — subcellular localization by immunofluorescence with functional knockdown and rescue, single lab\",\n      \"pmids\": [\"28189689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GCN2 regulates hepatic gluconeogenesis through regulation of C/EBPβ expression. Gcn2-deficient mice show reduced gluconeogenic capacity and failure to induce C/EBPβ during fasting; liver-specific Cebpβ knockout mice phenocopy the reduced fasting gluconeogenesis seen in Gcn2-deficient mice, placing GCN2 upstream of C/EBPβ in this pathway.\",\n      \"method\": \"Gcn2-/- mice, pyruvate tolerance test, gluconeogenic enzyme expression, TCA cycle intermediate measurement, C/EBPβ expression analysis, liver-specific Cebpβ KO mice\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with two knockout models and metabolic phenotyping, single lab\",\n      \"pmids\": [\"23900421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Drosophila GCN2 is required for 4E-BP transcriptional induction via ATF4; the 4E-BP intron contains ATF4-binding sites. GCN2 is required for lifespan extension in response to dietary amino acid restriction, and gcn2 mutant flies have reduced levels of stress-responsive protein synthesis as measured by metabolic labeling combined with click chemistry.\",\n      \"method\": \"GCN2 mutant Drosophila, 4E-BP reporter assays, ATF4 binding site analysis, metabolic labeling (click chemistry) for nascent protein synthesis, lifespan assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mutant with multiple molecular and phenotypic readouts, single organism model\",\n      \"pmids\": [\"27979906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In nutrient-rich conditions, GCN2 supports cancer cell proliferation by stimulating 47S rRNA transcription via nuclear translocation of methionyl-tRNA synthetase (MetRS). GCN2 inhibition prevents nuclear translocation of MetRS, causing nucleolar stress, mTORC1 inhibition, and autophagy induction. Under metabolic stress, GCN2 represses 47S rRNA expression through the canonical ISR axis.\",\n      \"method\": \"GCN2 inhibition (pharmacological and genetic), MetRS nuclear/cytoplasmic fractionation, 47S rRNA quantification, mTORC1 activity assay, autophagy assay, patient-derived tumoroids\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — pharmacological and genetic inhibition with MetRS localization and functional readouts, single lab\",\n      \"pmids\": [\"37452637\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"High MYC levels in APC-deficient colorectal cancer cells induce phosphorylation of eIF2α via GCN2 (and PKR), forming a negative feedback loop. Pharmacological inhibition of GCN2 phenocopies eIF2B5 depletion, causing MYC-dependent apoptosis and demonstrating therapeutic efficacy in patient-derived tumor organoids.\",\n      \"method\": \"GCN2 pharmacological inhibition, eIF2α phosphorylation assay, tumor organoid model, genetic epistasis (APC, MYC, GCN2)\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and genetic approaches in patient-derived models with defined pathway placement, single lab\",\n      \"pmids\": [\"31685988\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EIF2AK4/GCN2 is a serine/threonine eIF2α kinase that senses amino acid insufficiency primarily through its HisRS-like domain binding uncharged tRNAs (and via the ribosomal P-stalk) to relieve autoinhibition involving an inhibitory pseudokinase–kinase domain interaction, whereupon active GCN2 phosphorylates eIF2α at Ser-51 (suppressing bulk translation while preferentially translating ATF4/GCN4 mRNAs), and also phosphorylates additional substrates including eIF2β, Gcn20, FBXO22 (leading to mTOR ubiquitination), and HIV-1 integrase; GCN2 activity is regulated by Hsp90 chaperone, TOR/TAP42-dependent Ser-577 phosphorylation, Gcn1/Gcn20 co-activators, the Yih1/IMPACT inhibitor competing for Gcn1 binding, and mTOR-mediated phosphorylation at Ser-230, with diverse biological roles including antiviral defense, synaptic plasticity via the ATF4/CREB axis, angiogenesis, immune cell polarization, wound healing, HSC proteostasis, and when mutated (loss-of-function biallelic mutations), pulmonary veno-occlusive disease/pulmonary capillary hemangiomatosis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"EIF2AK4/GCN2 is a serine/threonine eIF2\\u03b1 kinase that functions as the central translational sensor of amino acid insufficiency, coupling nutrient and ribosomal stress to a programmed reduction in bulk protein synthesis and preferential translation of stress mRNAs [#11, #2]. Catalysis requires its conserved kinase domain, and active GCN2 phosphorylates eIF2\\u03b1 specifically at Ser-51 through recognition determinants that include residues flanking the phospho-acceptor and a distal surface in the K79GYID83 motif [#1, #2, #7]. Activation is gated by a bipartite tRNA-binding module formed by the HisRS-related domain plus a C-terminal ribosome-binding segment: uncharged tRNA binding relieves an inhibitory intramolecular interaction between the regulatory regions and the kinase, while aminoacylation weakens tRNA binding [#0, #2]. Crystallographic and biochemical work shows the resting kinase adopts an autoinhibited closed conformation, and that productive signaling additionally requires kinase-domain dimerization through a conserved intermolecular salt bridge, an interdigitated C-terminal dimer, and allosteric stimulation of the kinase by the pseudokinase (YKD) domain [#5, #8, #15, #16]. In mammals GCN2 is potently activated by the ribosomal P-stalk (uL10 and the P1/P2 C-terminal tails) and by ribosomal collisions, with distinct stress types\\u2014amino acid depletion versus elongation stalling\\u2014engaging uncharged-tRNA sensing or collision sensing respectively through the same HisRS-like domain [#10, #19, #20]. GCN2 activity is further set by the Hsp90 chaperone, TOR-dependent Ser-577 phosphorylation, and the Gcn1/Gcn20 co-activators that are antagonized by the Yih1/IMPACT competitor [#9, #6, #18], and GCN2 itself extends signaling beyond eIF2\\u03b1 by phosphorylating eIF2\\u03b2 to restrict ternary-complex recycling and by phosphorylating FBXO22 to drive K27-linked ubiquitination of mTOR at Lys-2066 and suppress mTORC1 [#17, #24]. Downstream, GCN2 acts largely through the ATF4 axis to control diverse processes\\u2014synaptic plasticity and memory via ATF4/CREB, tumor amino-acid adaptation and SLC transporter expression, angiogenesis via VEGF, myeloid and macrophage polarization, autophagy, wound-healing cell migration, and hematopoietic stem cell proteostasis [#13, #14, #27, #23, #25, #31, #26, #28]. GCN2 also functions in antiviral defense, restricting RNA and DNA viruses and directly phosphorylating HIV-1 integrase at Ser-255 [#12, #36, #22]. Biallelic loss-of-function mutations in EIF2AK4 underlie pulmonary veno-occlusive disease, where GCN2 deficiency derepresses collagen I via loss of ATF3-dependent p38 MAPK control [#37].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Establishing that GCN2 is a genuine protein kinase whose catalytic activity drives GCN4 induction defined the core of the general amino acid control pathway.\",\n      \"evidence\": \"Catalytic-lysine mutagenesis abolishing autophosphorylation and in vivo GCN4-lacZ regulation, plus deletion of flanking regulatory domains, in yeast\",\n      \"pmids\": [\"2188100\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physiological substrate not yet identified at this stage\", \"Mechanism by which flanking domains lower the tRNA-activation threshold unresolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Mapping eIF2\\u03b1 as the substrate and showing the HisRS-related domain is required for its phosphorylation linked nutrient sensing to translation initiation.\",\n      \"evidence\": \"Cell-free kinase assay on recombinant eIF2\\u03b1 with HisRS-domain point mutants, correlated to in vivo defects\",\n      \"pmids\": [\"8798780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish how the HisRS domain transmits signal to the kinase\", \"Structural basis of Ser-51 selectivity unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defining a bipartite tRNA-binding module that intramolecularly inhibits the kinase, relieved by uncharged tRNA, explained how amino acid status is decoded.\",\n      \"evidence\": \"In vitro binding of HisRS+C-term to the kinase domain, aminoacylation-dependent tRNA binding, and activating E803V mutant analysis; parallel demonstration that mouse GCN2 phosphorylates eIF2\\u03b1 at Ser-51\",\n      \"pmids\": [\"10983975\", \"10655230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational details of activation not resolved\", \"Whether mammalian and yeast activation modes are identical not addressed\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Demonstrating GCN2 association with 60S subunits and polysomes via its extreme C-terminus placed the kinase at the ribosome where deacylated tRNAs accumulate.\",\n      \"evidence\": \"Sucrose-gradient sedimentation, salt-dependent dissociation, and C-terminal deletion analysis in yeast\",\n      \"pmids\": [\"2038314\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular contact on the ribosome not identified\", \"Functional consequence of ribosome binding for activation not yet dissected\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Structural and dimer-interface studies revealed the activation logic of the kinase domain: a closed autoinhibited conformation relieved by hinge remodeling and obligatory dimerization.\",\n      \"evidence\": \"Crystal structures of WT and R794G kinase domains; charge-swap mutagenesis of a conserved dimer salt bridge across GCN2/PKR/PERK with in vitro and yeast validation; eIF2\\u03b1 surface-residue mutagenesis defining substrate recognition\",\n      \"pmids\": [\"15964839\", \"17202131\", \"15798194\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length activation conformation not visualized\", \"How HisRS/tRNA binding mechanically opens the kinase not directly observed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identifying TOR-driven Ser-577 phosphorylation and Hsp90 dependence showed GCN2 activity is set by upstream signaling and chaperone maturation, not tRNA alone.\",\n      \"evidence\": \"S577A mutagenesis with rapamycin/TAP42 epistasis (1999 Hsp90 work used reciprocal Co-IP, inhibitors, and ts mutants)\",\n      \"pmids\": [\"12654728\", \"10567567\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian conservation of Ser-577 control not tested here\", \"Kinase responsible for Ser-577 not directly identified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Knockout mice established GCN2 as the essential eIF2\\u03b1 kinase for amino acid deprivation in mammals, validating physiological relevance in vivo.\",\n      \"evidence\": \"Gcn2-/- ES cells and perfused liver failing to induce eIF2\\u03b1 phosphorylation under amino acid limitation, with dietary lethality phenotype\",\n      \"pmids\": [\"12215525\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific downstream programs not yet defined\", \"Non-eIF2\\u03b1 substrates not explored\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showing GCN2 senses viral RNA and restricts viral replication extended its sensor role beyond nutrients into innate antiviral defense.\",\n      \"evidence\": \"In vitro activation by Sindbis genomic RNA via the HisRS domain, plus GCN2-/- cells/mice with increased viral susceptibility and kinase-dead K618R rescue failure; later ENU loss-of-function mice showed susceptibility to DNA viruses\",\n      \"pmids\": [\"16601681\", \"22114338\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How viral RNA and tRNA inputs are distinguished by the same domain unclear\", \"Breadth of viral ligands not mapped\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Linking GCN2 to ATF4/CREB-dependent synaptic plasticity opened the neuronal arm of GCN2 signaling.\",\n      \"evidence\": \"Gcn2-/- mice with altered LTP, memory behavior, and reduced hippocampal ATF4\",\n      \"pmids\": [\"16121183\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Local translational targets in neurons not enumerated\", \"Activating stimulus in resting neurons not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Dissecting C-terminal dimerization and pseudokinase-kinase allostery revealed the intramolecular architecture coupling sensing domains to catalysis.\",\n      \"evidence\": \"Crystal structures of murine/yeast CTD dimers with disruption mutants, and YKD \\u03b1E/\\u03b1I mutagenesis modulating YKD-KD interaction and GCN4 reporter output\",\n      \"pmids\": [\"24719324\", \"24811037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian CTD does not stably bind ribosomes, leaving its in vivo role open\", \"Order of dimerization and tRNA-binding events not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identifying the ribosomal P-stalk as the principal mammalian activator and distinguishing collision- versus tRNA-driven activation reframed GCN2 as a ribosome-state sensor.\",\n      \"evidence\": \"In vitro reconstitution with purified P-stalk and HDX-MS (human); yeast genetic epistasis separating tethered-P-stalk from uncharged-tRNA activation; later domain/collision analysis across stresses\",\n      \"pmids\": [\"30804176\", \"37043534\", \"38281137\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of each input in cells under physiological stress not settled\", \"How P-stalk and tRNA signals converge structurally on the kinase unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defining Gcn1/Gcn20 co-activation and Yih1/IMPACT competition for Gcn1 established the activator/inhibitor checkpoint controlling GCN2 at ribosomes.\",\n      \"evidence\": \"RWD-domain mutagenesis and reciprocal binding assays (Yih1/IMPACT, 2011) and S. pombe tRNA-site and Gcn1-deletion epistasis across multiple stresses\",\n      \"pmids\": [\"21239490\", \"28771613\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry of the Gcn1/Gcn20/GCN2 complex on the ribosome not defined\", \"Cross-stress findings rely on genetic, not reconstituted, evidence\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery of non-eIF2\\u03b1 substrates (eIF2\\u03b2, Gcn20, FBXO22, HIV-1 integrase) broadened GCN2's output to direct control of ternary-complex recycling, feedback, mTORC1, and viral targets.\",\n      \"evidence\": \"Phosphoproteomics with eIF2\\u03b2-eIF5 and Gcn20 feedback validation; in vitro kinase/ubiquitination reconstitution for FBXO22\\u2192mTOR K2066; in vitro kinase mapping of HIV-1 integrase Ser-255 with infectivity assays\",\n      \"pmids\": [\"33743194\", \"37979583\", \"28536474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full substrate repertoire in mammalian cells not catalogued\", \"Relative physiological weighting of eIF2\\u03b1 versus alternative substrates unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mapping diverse downstream physiology placed GCN2/ATF4 upstream of amino-acid transport, angiogenesis, immune polarization, autophagy, migration, and stem-cell proteostasis.\",\n      \"evidence\": \"Genetic and pharmacological loss-of-function with in vivo models across tumors (SLC/transporters, MYC feedback), endothelium (VEGF), myeloid cells, intestinal autophagy (ATF4 ChIP), keratinocyte migration, and HSCs\",\n      \"pmids\": [\"29570992\", \"31836669\", \"26986695\", \"26986695\", \"34597669\", \"35803229\", \"36107759\", \"20473272\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether these effects are all ATF4-dependent or involve alternative substrates not uniformly resolved\", \"Tissue-specific activating signals not always defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defining bidirectional GCN2-mTOR crosstalk and paradoxical inhibitor-induced activation refined the pharmacology and regulatory wiring of the kinase.\",\n      \"evidence\": \"mTOR\\u2192GCN2 Ser-230 phosphorylation (Co-IP, in vitro kinase); ATP-competitive inhibitors (Gcn2iB, neratinib) that bind and activate GCN2, validated in patient-derived kinase-domain mutants and CRISPR screens\",\n      \"pmids\": [\"39013537\", \"36898579\", \"34949839\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ser-230 phosphorylation is single-lab and awaits independent confirmation\", \"Structural basis of inhibitor-induced activation not solved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Patient-derived models tied biallelic EIF2AK4 loss to pulmonary veno-occlusive disease through derepressed collagen I.\",\n      \"evidence\": \"CRISPR GCN2 KO lines and PVOD patient iPSC-derived smooth muscle cells showing ATF3/p38-dependent collagen I upregulation\",\n      \"pmids\": [\"33988041\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab mechanism not independently replicated\", \"Causal chain from eIF2\\u03b1/ATF4 to ATF3/p38 incompletely defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple activating inputs (uncharged tRNA, P-stalk/collisions, viral RNA, mTOR phosphorylation, kinase-directed inhibitors) are integrated into a single quantitative output, and how non-eIF2\\u03b1 substrate phosphorylation is prioritized in vivo, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model of full-length activated GCN2 on the ribosome\", \"Relative in vivo contribution of eIF2\\u03b1 versus eIF2\\u03b2/FBXO22 substrates unknown\", \"Mammalian conservation of several yeast-defined regulatory phosphosites not fully established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 2, 4, 7, 17, 22, 24]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 2, 24]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 12]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005840\", \"supporting_discovery_ids\": [3, 10, 19]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [41]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 11, 17]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [17]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [11, 14, 20]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [31, 38]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [25, 29]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [37]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"EIF2S1\", \"HSP90\", \"GCN1\", \"GCN20\", \"FBXO22\", \"MTOR\", \"IMPACT\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}