General Control Nonderepressible 2 Research Articles

GCN2-SLC7A11 axis coordinates autophagy, cell cycle and apoptosis and regulates cell growth in retinoblastoma upon arginine deprivation

BackgroundArginine deprivation was previously shown to inhibit retinoblastoma cell proliferation and induce cell death in vitro. However, the mechanisms by which retinoblastoma cells respond to arginine deprivation remain to be elucidated.MethodsThe human-derived retinoblastoma cell lines Y79 and WERI-Rb-1 were subjected to arginine depletion, and the effects on inhibiting cell growth and survival were evaluated. This study investigated potential mechanisms, including autophagy, cell cycle arrest and apoptosis. Moreover, the roles of the general control nonderepressible 2 (GCN2) and mechanistic target of rapamycin complex 1 (mTORC1) signaling pathways in these processes were examined.ResultsWe demonstrated that arginine deprivation effectively inhibited the growth of retinoblastoma cells in vitro. This treatment caused an increase in the autophagic response. Additionally, prolonged arginine deprivation induced G2 cell cycle arrest and was accompanied by an increase in early apoptotic cells. Importantly, arginine depletion also induced the activation of GCN2 and the inhibition of mTOR signaling. We also discovered that the activation of SLC7A11 was regulated by GCN2 upon arginine deprivation. Knockdown of SLC7A11 rendered retinoblastoma cells partially resistant to arginine deprivation. Furthermore, we found that knockdown of GCN2 led to a decrease in the autophagic response in WERI-Rb-1 cells and arrested more cells in S phase, which was accompanied by fewer apoptotic cells. Moreover, knockdown of GCN2 induced the constant expression of ATF4 and the phosphorylation of 70S6K and 4E-BP1 regardless of arginine deprivation.ConclusionsCollectively, our findings suggest that the GCN2‒SLC7A11 axis regulates cell growth and survival upon arginine deprivation through coordinating autophagy, cell cycle arrest, and apoptosis in retinoblastoma cells. This work paves the way for the development of a novel treatment for retinoblastoma.

The transcription factor CAMTA2 interacts with the histone acetyltransferase GCN5 and regulates grain weight in wheat.

Grain weight and size are major traits targeted in breeding to improve wheat (Triticum aestivum L.) yield. Here, we find that the histone acetyltransferase GENERAL CONTROL NONDEREPRESSIBLE 5 (GCN5) physically interacts with the calmodulin-binding transcription factor CAMTA2 and regulates wheat grain size and weight. gcn5 mutant grains were smaller and contained less starch. GCN5 promoted the expression of the starch biosynthesis genes SUCROSE SYNTHASE 2 (Sus2) and STARCH-BRANCHING ENZYME Ic (SBEIc) by regulating H3K9ac and H3K14ac levels in their promoters. Moreover, immunoprecipitation followed by mass spectrometry (IP-MS) revealed that CAMTA2 physically interacts with GCN5. The CAMTA2-GCN5 complex activated Sus2 and SBEIc by directly binding to their promoters and depositing H3K9ac and H3K14ac marks during wheat endosperm development. camta2 knockout mutants exhibited similar phenotypes to gcn5 mutants, including smaller grains that contained less starch. In gcn5 mutants, transcripts of high molecular weight (HMW) Glutenin (Glu) genes were downregulated, leading to reduced HMW glutenin protein levels, gluten content, and sodium dodecyl sulfate (SDS) sedimentation volume. However, the association of GCN5 with Glu genes was independent of CAMTA2, since GCN5 enrichment on Glu promoters was unchanged in camta2 knockouts. Finally, we identified a CAMTA2-AH3 elite allele that corresponded with enhanced grain size and weight, serving as a candidate gene for breeding wheat varieties with improved grain weight.

General control nonderepressible 2 (GCN2) as a therapeutic target in age-related diseases.

The function of General Control Nonderepressible 2 (GCN2), an evolutionary-conserved component of the integrated stress response (ISR), has been well-documented across organisms from yeast to mammals. Recently GCN2 has also gained attention for its role in health and disease states. In this review, we provide a brief overview of GCN2, including its structure, activation mechanisms and interacting partners, and explore its potential significance as a therapeutic target in various age-related diseases including neurodegeneration, inflammatory disorders and cancer. Finally, we summarize the barriers to effectively targeting GCN2 for the treatment of disease and to promote a healthier aging process.

IDO1 inhibitors are synergistic with CXCL10 agonists in inhibiting colon cancer growth

Indoleamine 2,3-dioxygenase 1 (IDO1) is an immune checkpoint that degrades L-tryptophan to kynurenine (Kyn) and enhance immunosuppression, which can be an attractive target for treating colon cancer. IDO1 inhibitors have limited efficacy when used as monotherapies, and their combination approach has been shown to provide synergistic benefits. Many studies have shown that targeting chemokines can promote the efficacy of immune checkpoint inhibitors. Therefore, this study explored the use of IDO1 inhibitors with multiple chemokines to develop a new combination regimen for IDO1 inhibitors. We found that IDO1 inhibitors reduce the secretion of C-X-C motif ligand 10(CXCL10) in cancer cells, and CXCL10 supplementation significantly improved the anticancer effect of IDO1 inhibitors. The combination of the IDO1 inhibitor with CXCL10 or its agonist axitinib had a synergistic inhibitory effect on the growth of colon cancer cells and transplanted CT26 tumors. This synergistic effect may be achieved by inhibiting cancer cell proliferation, promoting cancer cell apoptosis, promoting CD8+T cell differentiation and decreasing Tregs. Two downstream pathways of IDO1 affect CXCL10 secretion. One being the Kyn-aryl hydrocarbon receptor (AHR) pathway, the other is the general control nonderepressible 2(GCN2). Our study provides a new reference for combination regimens of IDO1 inhibitors.

GCN2 drives diurnal patterns in the hepatic integrated stress response and maintains circadian rhythms in whole body metabolism during amino acid insufficiency.

Disruptions in circadian rhythms are associated with an increased risk of developing metabolic diseases. General control nonderepressible 2 (GCN2), a primary sensor of amino acid insufficiency and activator of the integrated stress response (ISR), has emerged as a conserved regulator of the circadian clock in multiple organisms. The objective of this study was to examine diurnal patterns in hepatic ISR activation in the liver and whole body rhythms in metabolism. We hypothesized that GCN2 activation cues hepatic ISR signaling over a natural 24-h feeding-fasting cycle. To address our objective, wild-type (WT) and whole body Gcn2 knockout (GCN2 KO) mice were housed in metabolic cages and provided free access to either a control or leucine-devoid diet (LeuD) for 8 days in total darkness. On the last day, blood and livers were collected at CT3 (CT = circadian time) and CT15. In livers of WT mice, GCN2 phosphorylation followed a diurnal pattern that was guided by intracellular branched-chain amino acid concentrations (r2 = 0.93). Feeding LeuD to WT mice increased hepatic ISR activation at CT15 only. Diurnal oscillations in hepatic ISR signaling, the hepatic transcriptome including lipid metabolic genes, and triglyceride concentrations were substantially reduced or absent in GCN2 KO mice. Furthermore, mice lacking GCN2 were unable to maintain circadian rhythms in whole body energy expenditure, respiratory exchange ratio, and physical activity when fed LeuD. In conclusion, GCN2 activation functions to maintain diurnal ISR activation in the liver and has a vital role in the mechanisms by which nutrient stress affects whole body metabolism.NEW & NOTEWORTHY This work reveals that the eIF2 kinase GCN2 functions to support diurnal patterns in the hepatic integrated stress response during natural feeding and is necessary to maintain circadian rhythms in energy expenditure, respiratory exchange ratio, and physical activity during amino acid stress.

5 A Phase 1b, Open-Label, Safety, Tolerability, and Efficacy Study of HC-7366 in Combination with Belzutifan (WELIREGTM) in Patients with Advanced or Metastatic Renal Cell Carcinoma, NCT06234605

Abstract Background HC-7366 is a novel, orally administered, highly selective and potent activator of general control nonderepressible 2 (GCN2) kinase, a core regulator of metabolic stress through activation of the integrated stress response (ISR). Activation of GCN2 promotes cell survival, whereas prolonged activation induces apoptosis. GCN2 activation also suppresses general protein synthesis and induces cell cycle arrest, thereby preventing cell growth during nutrient scarcity. Additionally, HC-7366 decreases HIF expression and inhibits glycolysis, oxidative phosphorylation, and TCA cycle function. HC-7366 also inhibits HIF expression in immunosuppressive myeloid cells, including macrophages. These effects of HC-7366 on metabolism, HIF signaling, and immune suppression suggest therapeutic benefit in ccRCC with clear rationale for combinations with HIF2a antagonists and immune checkpoint inhibitors. HC-7366 (0.5-1 mg/kg), combined with belzutifan (1 mg/kg), exhibited combination benefit in HIF-2 dependent A-498 and 786-O RCC xenografts, yielding 90% tumor growth inhibition and a three-fold increase in complete responses, respectively. Additionally, HC-7366 drives significant monotherapy antitumor activity in PDX models that demonstrated belzutifan resistance. Mechanism of action studies have identified several pathway engagement and potential efficacy biomarkers (Stokes, et al., 2024). Trial design/schema This multicenter, open-label phase 1b study will identify the Maximum Tolerated Dose (MTD) and/or the Recommended Phase 2 Dose (RP2D) of HC-7366 in combination with fixed-dose belzutifan, 120 mg po qd, in patients with advanced or metastatic RCC with renal cell histology irrespective of VHL gene mutation. Monotherapy HC-7366 will be evaluated in parallel. The monotherapy arm, HC-7366, 60 mg p.o. qd, includes patients who have relapsed after 1 to 4 prior lines of standard of care that may include belzutifan or another HIF-2α inhibitor. The combination arm includes patients who have received 1 to 3 prior lines of standard of care and are belzutifan or HIF-2α naïve. HC-7366 dose escalation arm evaluates combination fixed dose belzutifan, 120 mg po qd plus HC-7366 at 20, 40, or 60 mg po qd. Enrollment will start with the HC-7366 monotherapy arm. Subsequently, patients will begin to enroll in the combination therapy HC-7366 dose escalation arm, while the monotherapy arm will continue to enroll. Expansion will evaluate the combination of fixed dose belzutifan with two doses of HC-7366 selected from escalation. Assessments include safety, PK, and anti-tumor activity. The study will enroll up to 80 patients at US study sites. Significance and vision Combination HC-7366 plus belzutifan, supported by preclinical evidence, is being studied to assess antitumor activity in the RCC relapsed setting. Determining safety and evaluation of dose are foundational to this study. Reference Stokes M, Tameire F, Wojnarowicz P, et al. HC-7366, a potent GCN2 activator, complements belzutifan, a HIF-2⍺ antagonist, by providing combination benefit in belzutifan-sensitive models and monotherapy activity in belzutifan-resistant models. Meeting of the American Association for Cancer Research; 2024 Apr 5-10; San Diego (CA); AACR; 2024. Abstract 4615. This study is in collaboration with Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA

Computational modeling of the synergistic role of GCN2 and the HPA axis in regulating the integrated stress response in the central circadian timing system.

The circadian timing system and integrated stress response (ISR) systems are fundamental regulatory mechanisms that maintain body homeostasis. The central circadian pacemaker in the suprachiasmatic nucleus (SCN) governs daily rhythms through interactions with peripheral oscillators via the hypothalamus-pituitary-adrenal (HPA) axis. On the other hand, ISR signaling is pivotal for preserving cellular homeostasis in response to physiological changes. Notably, disrupted circadian rhythms are observed in cases of impaired ISR signaling. In this work, we examine the potential interplay between the central circadian system and the ISR, mainly through the SCN and HPA axis. We introduce a semimechanistic mathematical model to delineate SCN's capacity for indirectly perceiving physiological stress through glucocorticoid-mediated feedback from the HPA axis and orchestrating a cellular response via the ISR mechanism. Key components of our investigation include evaluating general control nonderepressible 2 (GCN2) expression in the SCN, the effect of physiological stress stimuli on the HPA axis, and the interconnected feedback between the HPA and SCN. Simulation revealed a critical role for GCN2 in linking ISR with circadian rhythms. Experimental findings have demonstrated that a Gcn2 deletion in mice leads to rapid re-entrainment of the circadian clock following jetlag as well as to an elongation of the circadian period. These phenomena are well replicated by our model, which suggests that both the swift re-entrainment and prolonged period can be ascribed to a reduced robustness in neuronal oscillators. Our model also offers insights into phase shifts induced by acute physiological stress and the alignment/misalignment of physiological stress with external light-dark cues. Such understanding aids in strategizing responses to stressful events, such as nutritional status changes and jetlag.NEW & NOTEWORTHY This study is the first theoretical work to investigate the complex interaction between integrated stress response (ISR) sensing and central circadian rhythm regulation, encompassing the suprachiasmatic nucleus (SCN) and hypothalamus-pituitary-adrenal (HPA) axis. The findings carry implications for the development of dietary or pharmacological interventions aimed at facilitating recovery from stressful events, such as jetlag. Moreover, they provide promising prospects for potential therapeutic interventions that target circadian rhythm disruption and various stress-related disorders.

A PDE3A-SLFN12 Molecular Glue Exhibits Significant Antitumor Activity in TKI-Resistant Gastrointestinal Stromal Tumors.

Gastrointestinal stromal tumor (GIST), the most common mesenchymal tumor with KIT or PDGFRA driver mutations, is typically treated with tyrosine kinase inhibitors (TKI). However, resistance to TKIs due to secondary mutations is a common challenge in advanced GISTs. In addition, there are currently no effective therapies for several other molecular subtypes, such as succinate dehydrogenase-deficient GISTs. Therefore, novel therapeutic strategies are needed. To address this need, we tested the efficacy of a novel non-TKI compound, OPB-171775, using patient-derived xenograft models of GISTs. In parallel, we sought to elucidate the mechanism of action of the compound. Our study revealed that OPB-171775 exhibited significant efficacy against GISTs regardless of their KIT mutation status by inducing complex formation between phosphodiesterase 3A (PDE3A) and Schlafen family member 12 (SLFN12), which are highly expressed in GISTs, leading to SLFN12 RNase-mediated cell death. Furthermore, we identified the activation of general control non-derepressible 2 and its downstream response as an effector pathway of SLFN12 in mediating anticancer activity and revealed potential pharmacodynamic markers. These findings suggest that OPB-171775, with its significant efficacy, could potentially serve as a novel and effective treatment option for advanced GISTs, particularly those resistant to TKIs.

Inhalation of hydrogen gas protects against mitomycin-induced pulmonary veno-occlusive disease

BackgroundAs a subtype of pulmonary hypertension (PH), pulmonary veno-occlusive disease (PVOD) is devastating and life-threatening disease without effective therapy. Hydrogen has been reported to exhibits antioxidant and anti-inflammatory effects in a rat model induced by monocrotaline of PH. In this study, we investigated the effects of inhaled hydrogen gas on the prevention and treatment of PVOD induced by mitomycin C (MMC) in rats.MethodsPVOD was induced in female Sprague-Dawley rats through intraperitoneal injection of MMC at a concentration of 3 mg·kg− 1·wk− 1 for 2 weeks. Inhalation of hydrogen gas (H2) was administered through a designed rat cage concurrently or two weeks after MMC administration. The severity of PVOD was assessed by using hemodynamic measurements and histological analysis. The expression levels of general control nonderepressible 2 (GCN2), nuclear factor erythroid 2-related factor-2 (Nrf2), heme oxygenase-1 (HO-1) and endothelial-to-mesenchymal transition (EndoMT) related proteins in lung tissue were measured. Levels of lipid peroxidation pro-inflammatory cytokines in serum were determined.ResultsInhaled H2 improved hemodynamics and right heart function, reversed right ventricular hypertrophy, and prevented pulmonary vessel reconstitution in both prevention and treatment approaches. It decreased malondialdehyde (MDA) levels in the serum and the expression of NADPH oxidase 1 (NOX-1) in lung tissue. It regulated Nrf2/HO-1 signaling pathway and anti-inflammatory factor GCN2 in lung tissue, accompanied by a decrease in macrophages and pro-inflammatory cytokines. Our data suggested that H2 inhalation effectively countered EndoMT induced by MMC, as evidenced by the detection of endothelial markers (e.g., VE-cadherin and CD31) and mesenchymal markers (e.g., vimentin and fibronectin). Further research revealed that H2 preserved p-Smad3 and induced p-Smad1/5/9.ConclusionInhalation of H2 effectively inhibits the pathogenesis of PVOD induced by MMC in rats. This inhibitory effect may be attributed to the antioxidant and anti-inflammatory properties of H2.

IDO1 Inhibitor RY103 Suppresses Trp-GCN2-Mediated Angiogenesis and Counters Immunosuppression in Glioblastoma.

Glioma is characterized by strong immunosuppression and excessive angiogenesis. Based on existing reports, it can be speculated that the resistance to anti-angiogenic drug vascular endothelial growth factor A (VEGFA) antibody correlates to the induction of novel immune checkpoint indoleamine 2,3-dioxygenase 1 (IDO1), while IDO1 has also been suggested to be related to tumor angiogenesis. Herein, we aim to clarify the potential role of IDO1 in glioma angiogenesis and the mechanism behind it. Bioinformatic analyses showed that the expressions of IDO1 and angiogenesis markers VEGFA and CD34 were positively correlated and increased with pathological grade in glioma. IDO1-overexpression-derived-tryptophan depletion activated the general control nonderepressible 2 (GCN2) pathway and upregulated VEGFA in glioma cells. The tube formation ability of angiogenesis model cells could be inhibited by IDO1 inhibitors and influenced by the activity and expression of IDO1 in condition medium. A significant increase in serum VEGFA concentration and tumor CD34 expression was observed in IDO1-overexpressing GL261 subcutaneous glioma-bearing mice. IDO1 inhibitor RY103 showed positive anti-tumor efficacy, including the anti-angiogenesis effect and upregulation of natural killer cells in GL261 glioma-bearing mice. As expected, the combination of RY103 and anti-angiogenesis agent sunitinib was proved to be a better therapeutic strategy than either monotherapy.

Toll-Like Receptors Mediate Opposing Dendritic Cell Effects on Treg/Th17 Balance in Mice With Intracerebral Hemorrhage.

Dendritic cells (DCs) regulate the immune response associated with T lymphocytes, but their role in stroke remains unclear. In this study, we investigated the causal relationship between DCs and T-cell response in intracerebral hemorrhage (ICH) by focusing on TLRs (toll-like receptors) that may modulate the function of DCs. We studied the effects of TLR4, TLR2, and TLR9 on DC-mediated T-cell response and the outcomes of ICH using male C57BL/6 and CD11c-DTx (diphtheria toxin) receptor mice. We administered specific agents intraperitoneally or orally and evaluated the results using flow cytometry, real-time polymerase chain reaction, Western blotting, immunofluorescence staining, histopathology, and behavioral tests. TLR4 and TLR2 activation induces DC maturation and reduces the ratio of regulatory T to T-helper 17 cells in the brain and periphery after ICH. When either of these receptors is activated, it can worsen neuroinflammation and exacerbate ICH outcomes. TLR9 also promotes DC maturation, stabilizing the number of DCs, particularly conventional DCs. TLR9 has the opposite effects on regulatory T/T-helper 17 balance, neuroinflammation, and ICH outcomes compared with TLR4 and TLR2. Upon stimulation, TLR4 and TLR9 may achieve these effects through the p38-MAPK (p38-mitogen-activated protein kinase)/MyD88 (myeloid differentiation primary response gene 88) and indoleamine 2,3-dioxygenase 1 (IDO1)/GCN2 (general control nonderepressible 2) signaling pathways, respectively. DCs act as intermediaries for TLR-mediated T-cell response. TLR-mediated opposing effects of DCs on T-cell response may provide novel strategies to treat ICH.

Gibberellin Signaling through RGA Suppresses GCN5 Effects on Arabidopsis Developmental Stages.

Histone acetyltransferases (HATs) modify the amino-terminal tails of the core histone proteins via acetylation, regulating chromatin structure and transcription. GENERAL CONTROL NON-DEREPRESSIBLE 5 (GCN5) is a HAT that specifically acetylates H3K14 residues. GCN5 has been associated with cell division and differentiation, meristem function, root, stem, foliar, and floral development, and plant environmental response. The flowers of gcn5 plants display a reduced stamen length and exhibit male sterility relative to the wild-type plants. We show that these effects may arise from gibberellin (GA)-signaling defects. The signaling pathway of bioactive GAs depends on the proteolysis of their repressors, DELLA proteins. The repressor GA (RGA) DELLA protein represses plant growth, inflorescence, and flower and seed development. Our molecular data indicate that GCN5 is required for the activation and H3K14 acetylation of genes involved in the late stages of GA biosynthesis and catabolism. We studied the genetic interaction of the RGA and GCN5; the RGA can partially suppress GCN5 action during the whole plant life cycle. The reduced elongation of the stamen filament of gcn5-6 mutants is reversed in the rga-t2;gcn5-6 double mutants. RGAs suppress the GCN5 effect on the gene expression and histone acetylation of GA catabolism and GA signaling. Interestingly, the RGA and RGL2 do not suppress ADA2b function, suggesting that ADA2b acts downstream of GA signaling and is distinct from GCN5 activity. In conclusion, we propose that the action of GCN5 on stamen elongation is partially mediated by RGA and GA signaling.

The Integrated Stress Response Regulates Diurnal Rhythms in Liver Metabolism

Disruptions in biological rhythms are associated with the development of metabolic diseases. General control nonderepressible 2 (GCN2), a primary sensor of amino acid insuffciency and activator of the integrated stress response (ISR), plays an integral role in liver metabolism. The objective of this work was to examine the impact of feeding a low protein quality (LPQ) diet on diurnal rhythms in liver metabolism. We hypothesized that activation of the ISR by GCN2 maintains metabolic rhythms within the liver during LPQ feeding. To address our objective, wild type (WT) and whole body Gcn2 knockout (GCN2KO) mice were housed in total darkness and provided free access to either a Control or a LPQ diet (devoid of leucine) for 8-days and then killed at 2 circadian time (CT) points 12-hours apart (CT3, CT15). WT mice fed a Control diet showed oscillations in hepatic ISR activation that were lost in the livers of GCN2KO mice. Diurnal patterns in the liver transcriptome including genes regulating triglyceride metabolism were also dampened in GCN2KO mice. WT mice fed LPQ showed increased hepatic ISR activation and greater abundance of ISR target genes relative to Control only at CT15 (p<0.05 by two factor ANOVA). GCN2KO mice fed LPQ failed to show oscillations in ISR activation and instead displayed reductions in liver intracellular amino acids alongside significant upregulation of genes encoding gluconeogenesis and amino acid catabolism at CT15 (q<0.05, Log2FC>1). In conclusion, GCN2 is required for diurnal ISR activation and execution in the liver. LPQ feeding increases hepatic ISR activation in a time dependent manner. Sensing of LPQ by GCN2 is necessary for the maintenance of rhythms in liver macronutrient metabolism. NIH DK109714, Pilot award from the NJ IFNH Center for Human Nutrition, Exercise, and Metabolism (NExT). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Odds of Protein Translation Control Under Stress.

Physical or chemical stress is commonly known to inhibit protein translation at the cellular level. Since the process of protein translation requires catalysis by a multi-component machinery containing eukaryotic initiation factors (eIFs) and ribosomes in a sequence of reactions, how the process fails to proceed and whether certain genes can escape such blockade have provoked research efforts. Lines of evidence have demonstrated that phosphorylation of eIF4E or dephosphorylation of 4E-binding proteins (4E-BPs) prevents the formation of the eukaryotic translation initiation factor 4F (eIF4F) complex, whereas phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α) due to activation of heme-regulated inhibitor (HRI), general control nonderepressible 2 (GCN2), protein kinase RNA-like endoplasmic reticulum kinase (PERK), or protein kinase R (PKR) by a diverse array of stressors prevents eIF2-GTP-tRNAiMet ternary complex assembly. These signal the abandonment of translation initiation via 5'-7-methylguanine (m7G) cap recognition by eIF4E. Stress can promote cleavage of tRNAs, impediment of rRNA processing, changes in the epitranscriptomic landscape, ribosome stalling or collision, activation of ribosomal surveillance systems, and assembly of the stress granules. Although these events contribute to the general inhibition of protein translation, a few proteins can bypass such negativity and become translated selectively. Such selective protein translation is primarily m7G cap independent through the integrated stress response or Internal Ribosomal Entry Site (IRES). The newly synthesized proteins often influence cell fate, facilitate cell survival, and build endogenous defense. Insights into the general inhibition of protein translation and selective translation of specific proteins will advance our understanding of the etiology or progression of human diseases involving cellular stress from viral infection or inflammation to myocardial infarction, stroke, or neurodegenerative disease. Antioxid. Redox Signal. 40, 943-947.

NtGCN2 confers cadmium tolerance in Nicotiana tabacum L. by regulating cadmium uptake, efflux, and subcellular distribution

General control non-derepressible-2 (GCN2) is widely expressed in eukaryotes and responds to biotic and abiotic stressors. However, the precise function and mechanism of action of GCN2 in response to cadmium (Cd) stress in Nicotiana tabacum L. (tobacco) remains unclear. We investigated the role of NtGCN2 in Cd tolerance and explored the mechanism by which NtGCN2 responds to Cd stress in tobacco by exposing NtGCN2 transgenic tobacco lines to different concentrations of CdCl2. NtGCN2 was activated under 50 μmol·L−1 CdCl2 stress and enhanced the Cd tolerance and photosynthetic capacities of tobacco by increasing chlorophyll content and antioxidant capacity by upregulating NtSOD, NtPOD, and NtCAT expression and corresponding enzyme activities and decreasing malondialdehyde and O2·- contents. NtGCN2 enhanced the osmoregulatory capacity of tobacco by elevating proline (Pro) and soluble sugar contents and maintaining low levels of relative conductivity. Finally, NtGCN2 enhanced Cd tolerance in tobacco by reducing Cd uptake and translocation, promoting Cd efflux, and regulating Cd subcellular distribution. In conclusion, NtGCN2 improves the tolerance of tobacco to Cd through a series of mechanisms, namely, increasing antioxidant, photosynthetic, and osmoregulation capacities and regulating Cd uptake, translocation, efflux, and subcellular distribution. This study provides a scientific basis for further exploration of the role of NtGCN2 in plant responses to Cd stress and enhancement of the Cd stress signaling network in tobacco.

Discovery of HC-7366: An Orally Bioavailable and Efficacious GCN2 Kinase Activator.

A series of activators of GCN2 (general control nonderepressible 2) kinase have been developed, leading to HC-7366, which has entered the clinic as an antitumor therapy. Optimization resulted in improved permeability compared to that of the original indazole hinge binding scaffold, while maintaining potency at GCN2 and selectivity over PERK (protein kinase RNA-like endoplasmic reticulum kinase). The improved ADME properties of this series led to robust in vivo compound exposure in both rats and mice, allowing HC-7366 to be dosed in xenograft models, demonstrating that activation of the GCN2 pathway by this compound leads to tumor growth inhibition.

Integrated Stress Response Potentiates Ponatinib-Induced Cardiotoxicity.

Mitochondrial dysfunction is a primary driver of cardiac contractile failure; yet, the cross talk between mitochondrial energetics and signaling regulation remains obscure. Ponatinib, a tyrosine kinase inhibitor used to treat chronic myeloid leukemia, is among the most cardiotoxic tyrosine kinase inhibitors and causes mitochondrial dysfunction. Whether ponatinib-induced mitochondrial dysfunction triggers the integrated stress response (ISR) to induce ponatinib-induced cardiotoxicity remains to be determined. Using human induced pluripotent stem cells-derived cardiomyocytes and a recently developed mouse model of ponatinib-induced cardiotoxicity, we performed proteomic analysis, molecular and biochemical assays to investigate the relationship between ponatinib-induced mitochondrial stress and ISR and their role in promoting ponatinib-induced cardiotoxicity. Proteomic analysis revealed that ponatinib activated the ISR in cardiac cells. We identified GCN2 (general control nonderepressible 2) as the eIF2α (eukaryotic translation initiation factor 2α) kinase responsible for relaying mitochondrial stress signals to trigger the primary ISR effector-ATF4 (activating transcription factor 4), upon ponatinib exposure. Mechanistically, ponatinib treatment exerted inhibitory effects on ATP synthase activity and reduced its expression levels resulting in ATP deficits. Perturbed mitochondrial function resulting in ATP deficits then acts as a trigger of GCN2-mediated ISR activation, effects that were negated by nicotinamide mononucleotide, an NAD+ precursor, supplementation. Genetic inhibition of ATP synthase also activated GCN2. Interestingly, we showed that the decreased abundance of ATP also facilitated direct binding of ponatinib to GCN2, unexpectedly causing its activation most likely because of a conformational change in its structure. Importantly, administering an ISR inhibitor protected human induced pluripotent stem cell-derived cardiomyocytes against ponatinib. Ponatinib-treated mice also exhibited reduced cardiac function, effects that were attenuated upon systemic ISRIB administration. Importantly, ISRIB does not affect the antitumor effects of ponatinib in vitro. Neutralizing ISR hyperactivation could prevent or reverse ponatinib-induced cardiotoxicity. The findings that compromised ATP production potentiates GCN2-mediated ISR activation have broad implications across various cardiac diseases. Our results also highlight an unanticipated role of ponatinib in causing direct activation of a kinase target despite its role as an ATP-competitive kinase inhibitor.

General Control Non-derepressible 2 Alleviates Cartilage Degeneration and Inhibits NLRP3 Inflammasome Activation in Osteoarthritis.

This study aimed to evaluate the effects of general control non-derepressible 2 (GCN2) on osteoarthritis (OA) in vivo and in vitro. First, anterior cruciate ligament transection (ACLT)-induced rat model and interleukin (IL)-1β-induced ATDC5 chondrocyte were established. Hematoxylin and eosin staining and safranin O/fast green staining were employed for analyzing the histological changes in the rat cartilage. In addition, immunohistochemistry, quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, western blot, and immunofluorescence staining were employed for examining cartilage degeneration-, inflammation-, autophagy-, and NLR family pyrin domain containing 3 (NLRP3) inflammasome-associated genes expression. Moreover, 2,7-dichlorodihydrofluorescein acetoacetic acid probe was utilized for examining the intracellular reactive oxygen species. In addition, 5-ethynyl-2'-deoxyuridine assay and flow cytometry were applied for detecting chondrocyte proliferation and apoptosis IL-1β-treated ATDC5 chondrocytes. GCN2 overexpression ameliorated articular cartilage degeneration and inflammation but promoted chondrocyte autophagy in ACLT-induced OA rats. Similarly, we demonstrated that the upregulation of GCN2 could promote chondrocyte proliferation, suppress chondrocyte apoptosis, attenuate chondrocyte inflammation and extracellular matrix degradation, and promote chondrocyte autophagy. Moreover, GCN2 overexpression could inhibit the activation of NLRP3 inflammasome in IL-1β-induced ATDC5 chondrocyte. Furthermore, 3-methyladenine neutralized the protective and autophagy-promoting effects of GCN2 overexpression on ATDC5 chondrocytes. GCN2 could attenuate inflammation and cartilage degeneration, promote chondrocyte autophagy, and inhibit NLRP3 inflammasome activation in OA.

Downregulation of nutrition sensor GCN2 in macrophages contributes to poor wound healing in diabetes

Poor skin wound healing, which is common in patients with diabetes, is related to imbalanced macrophage polarization. Here, we find that nutrition sensor GCN2 (general control nonderepressible 2) and its downstream are significantly upregulated in human skin wound tissue and mouse skin wound macrophages, but skin wound-related GCN2 expression and activity are significantly downregulated by diabetes and hyperglycemia. Using wound healing models of GCN2-deleted mice, bone marrow chimeric mice, and monocyte-transferred mice, we show that GCN2 deletion in macrophages significantly delays skin wound healing compared with wild-type mice by altering M1 and M2a/M2c polarization. Mechanistically, GCN2 inhibits M1 macrophages via OXPHOS-ROS-NF-κB pathway and promotes tissue-repairing M2a/M2c macrophages through eukaryotic translation initiation factor 2 (eIF2α)-hypoxia-inducible factor 1α (HIF1α)-glycolysis pathway. Importantly, local supplementation of GCN2 activator halofuginone efficiently restores wound healing in diabetic mice with re-balancing M1 and M2a/2c polarization. Thus, the decreased macrophage GCN2 expression and activity contribute to poor wound healing in diabetes and targeting GCN2 improves wound healing in diabetes.

The integrated stress response protects against ER stress but is not required for altered translation and lifespan from dietary restriction in Caenorhabditis elegans.

The highly conserved integrated stress response (ISR) reduces and redirects mRNA translation in response to certain forms of stress and nutrient limitation. It is activated when kinases phosphorylate a key residue in the alpha subunit of eukaryotic translation initiation factor 2 (eIF2). General Control Nonderepressible-2 (GCN2) is activated to phosphorylate eIF2α by the presence of uncharged tRNA associated with nutrient scarcity, while protein kinase R-like ER kinase-1 (PERK) is activated during the ER unfolded protein response (UPRER). Here, we investigated the role of the ISR during nutrient limitation and ER stress with respect to changes in protein synthesis, translationally driven mRNA turnover, and survival in Caenorhabditis elegans. We found that, while GCN2 phosphorylates eIF2α when nutrients are restricted, the ability to phosphorylate eIF2α is not required for changes in translation, nonsense-mediated decay, or lifespan associated with dietary restriction (DR). Interestingly, loss of both GCN2 and PERK abolishes increased lifespan associated with dietary restriction, indicating the possibility of other substrates for these kinases. The ISR was not dispensable under ER stress conditions, as demonstrated by the requirement for PERK and eIF2α phosphorylation for decreased translation and wild type-like survival. Taken together, results indicate that the ISR is critical for ER stress and that other translation regulatory mechanisms are sufficient for increased lifespan under dietary restriction.