Project description:The integrated stress response (ISR) controls cellular adaptations to nutrient deprivation, redox imbalances and ER stress. ISR genes are upregulated in stressed cells, primarily by the bZIP transcription factor ATF4 through its recruitment to cis-regulatory C/EBP:ATF response elements (CAREs) together with a dimeric partner of uncertain identity. Here we show that C/EBPγ:ATF4 heterodimers, but not C/EBPβ:ATF4 dimers, are the predominant CARE binding species in stressed cells. C/EBPγ and ATF4 associate with genomic CAREs in a mutually-dependent manner and co-regulate many ISR genes. By contrast, the C/EBP family members C/EBPβ and CHOP were largely dispensable for induction of stress genes. Cebpgâ??/â?? MEFs proliferate poorly and exhibit oxidative stress due to reduced glutathione levels and impaired expression of several glutathione biosynthesis pathway genes. Cebpgâ??/â?? mice (C57BL/6 background) display reduced body size and microphthalmia, similar to ATF4-null animals. In addition, C/EBPγ-deficient newborns die from atelectasis and respiratory failure which can be mitigated by in utero exposure to the anti-oxidant, N-acetyl-cysteine. Cebpgâ??/â?? mice on a mixed strain background show improved viability but, upon aging, develop significantly fewer malignant solid tumors compared to WT animals. Our findings identify C/EBPγ as a novel anti-oxidant regulator and an obligatory ATF4 partner that controls redox homeostasis in normal and cancerous cells. WT, Atf4-/-, and Cebpg-/- MEFs (passage 3) were cultured under normal and AAD conditions. RNA from each treatment condition was collected in triplicate for hybrization on Affymetrix Mouse Genome 430 2.0 microarrays.
Project description:The integrated stress response (ISR) controls cellular adaptations to nutrient deprivation, redox imbalances and ER stress. ISR genes are upregulated in stressed cells, primarily by the bZIP transcription factor ATF4 through its recruitment to cis-regulatory C/EBP:ATF response elements (CAREs) together with a dimeric partner of uncertain identity. Here we show that C/EBPγ:ATF4 heterodimers, but not C/EBPβ:ATF4 dimers, are the predominant CARE binding species in stressed cells. C/EBPγ and ATF4 associate with genomic CAREs in a mutually-dependent manner and co-regulate many ISR genes. By contrast, the C/EBP family members C/EBPβ and CHOP were largely dispensable for induction of stress genes. Cebpg−/− MEFs proliferate poorly and exhibit oxidative stress due to reduced glutathione levels and impaired expression of several glutathione biosynthesis pathway genes. Cebpg−/− mice (C57BL/6 background) display reduced body size and microphthalmia, similar to ATF4-null animals. In addition, C/EBPγ-deficient newborns die from atelectasis and respiratory failure which can be mitigated by in utero exposure to the anti-oxidant, N-acetyl-cysteine. Cebpg−/− mice on a mixed strain background show improved viability but, upon aging, develop significantly fewer malignant solid tumors compared to WT animals. Our findings identify C/EBPγ as a novel anti-oxidant regulator and an obligatory ATF4 partner that controls redox homeostasis in normal and cancerous cells.
Project description:The integrated stress response (ISR) controls cellular adaptations to nutrient deprivation, redox imbalances and ER stress. ISR genes are upregulated in stressed cells, primarily by the bZIP transcription factor ATF4 through its recruitment to cis-regulatory C/EBP:ATF response elements (CAREs) together with a dimeric partner of uncertain identity. Here we show that C/EBPγ:ATF4 heterodimers, but not C/EBPβ:ATF4 dimers, are the predominant CARE binding species in stressed cells. C/EBPγ and ATF4 associate with genomic CAREs in a mutually-dependent manner and co-regulate many ISR genes. By contrast, the C/EBP family members C/EBPβ and CHOP were largely dispensable for induction of stress genes. Cebpg−/− MEFs proliferate poorly and exhibit oxidative stress due to reduced glutathione levels and impaired expression of several glutathione biosynthesis pathway genes. Cebpg−/− mice (C57BL/6 background) display reduced body size and microphthalmia, similar to ATF4-null animals. In addition, C/EBPγ-deficient newborns die from atelectasis and respiratory failure which can be mitigated by in utero exposure to the anti-oxidant, N-acetyl-cysteine. Cebpg−/− mice on a mixed strain background show improved viability but, upon aging, develop significantly fewer malignant solid tumors compared to WT animals. Our findings identify C/EBPγ as a novel anti-oxidant regulator and an obligatory ATF4 partner that controls redox homeostasis in normal and cancerous cells.
Project description:Oncogenic signals often activate abnormal proliferation, while simultaneously activate stress-adaptive mechanisms such as the integrated stress response (ISR) to ensure rapid growth under intrinsic and extrinsic stress conditions. In this study, we investigated the involvement of EGFR-PI3K pathway in the regulation of ISR in EGFR-mutant NSCLC cell lines under amino acid deprivation. We found that the third generation EGFR inhibitor osiemrtinib suppressed induction of activation transcription factor 4 (ATF4), the key ISR effector, in EGFR mutant cells, while the effect was to a less extent in cells harboring PIK3CA-co-alteration. PI3K inhibitors including P110a-specific inhibitor alpelicib markedly suppress ATF4 induction in PIK3CA-mutant cell lines. To further explore the role of EGFR-PI3K, transcriptome analysis was performed in EGFR- and PIK3CA-mutated NCI-H1975 cells treated with osimertinib, alpelisib, or combination of these in the absence or presence of histidyl-tRNA inhibitor L-histidinol (His), mimicking amino acid deprived conditions. Among His-induced genes, either osimertinib or alpelisib partially, but the combination dramatically suppressed a cluster of genes targeted by ATF4. Furthermore, combination of osimertinib and alpelisib increased apoptotic cells under amino acid deprived conditions. These results indicate that oncogenic EGFR-PI3K pathway contributes to cellular adaptation to stress conditions through ATF4. We used microarrays to identify genes whose expression is up- or down-regulated by inhibition of EGFR, PI3K, or both under amino acid deprivation.
Project description:Activating Transcription Factor 4 (ATF4) is a transcription factor induced by the integrated stress response (ISR). This experiment is a genome-wide profiling of ATF4-dependent RNA expression in human HAP-1 cells. HAP-1 is a near-haploid human cell line that was derived from KBM-7 cells isolated from a patient with Chronic Myelogenous Leukemia. We analyzed WT and ATF4 KO cells. We induced ATF4 expression by mimicking amino acid starvation with the drug histidinol. RNA expression profiles were generated for WT and ATF4 KO HAP1 cells. ATF4 genes were mutated using Cas9 genome editing technology. Amino acid starvation was mimicked by treating WT and ATF4 KO cells with 2 mM histidinol for 24 hours, which increases ATF4 expression.
Project description:Besides being building blocks for protein synthesis, amino acids serve a wide variety of cellular functions, including acting as metabolic intermediates for ATP generation and for redox homeostasis. Upon amino acid deprivation, free uncharged tRNAs trigger GCN2-ATF4 to mediate the well-characterized transcriptional amino acid response (AAR). However, it is not clear whether the deprivation of different individual amino acids triggers identical or distinct AARs. Here, we characterized the global transcriptional response upon deprivation of one amino acid at a time. With the exception of glycine, which was not required for the proliferation of MCF7 cells, we found that the deprivation of most amino acids triggered a shared transcriptional response that included the activation of ATF4, p53 and TXNIP. However, there was also significant heterogeneity among different individual AARs. The most dramatic transcriptional response was triggered by methionine deprivation, which activated an extensive and unique response in different cell types. We uncovered that the specific methionine-deprived transcriptional response required creatine biosynthesis. This dependency on creatine biosynthesis was caused by the consumption of S-Adenosyl-L-methionine (SAM) during creatine biosynthesis that helps to deplete SAM under methionine deprivation and reduces histone methylations. As such, the simultaneous deprivation of methionine and sources of creatine biosynthesis (either arginine or glycine) abolished the reduction of histone methylation and the methionine-specific transcriptional response. Arginine-derived ornithine was also required for the complete induction of the methionine-deprived specific gene response. Collectively, our data identify a previously unknown set of heterogeneous amino acid responses and reveal a distinct methionine-deprived transcriptional response that results from the crosstalk of arginine, glycine and methionine metabolism via arginine/glycine-dependent creatine biosynthesis. RNA was extracted by RNAeasy kits (Qiagen) from the MCF7 or PC3 cells which exposed to the control full DMEM or deprived one (or all) amino acid media for 24 or 48 hours.
Project description:The integrated stress response (ISR) controls cellular adaptations to nutrient deprivation, redox imbalances and ER stress. ISR genes are upregulated in stressed cells, primarily by the bZIP transcription factor ATF4 through its recruitment to cis-regulatory C/EBP:ATF response elements (CAREs) together with a dimeric partner of uncertain identity. Here we show that C/EBPγ:ATF4 heterodimers, but not C/EBPβ:ATF4 dimers, are the predominant CARE binding species in stressed cells. C/EBPγ and ATF4 associate with genomic CAREs in a mutually-dependent manner and co-regulate many ISR genes. By contrast, the C/EBP family members C/EBPβ and CHOP were largely dispensable for induction of stress genes. Cebpgâ/â MEFs proliferate poorly and exhibit oxidative stress due to reduced glutathione levels and impaired expression of several glutathione biosynthesis pathway genes. Cebpgâ/â mice (C57BL/6 background) display reduced body size and microphthalmia, similar to ATF4-null animals. In addition, C/EBPγ-deficient newborns die from atelectasis and respiratory failure which can be mitigated by in utero exposure to the anti-oxidant, N-acetyl-cysteine. Cebpgâ/â mice on a mixed strain background show improved viability but, upon aging, develop significantly fewer malignant solid tumors compared to WT animals. Our findings identify C/EBPγ as a novel anti-oxidant regulator and an obligatory ATF4 partner that controls redox homeostasis in normal and cancerous cells. Evaluation of genomic binding of 2 bZIP transcription factors under amino acid deprivation conditions in mouse embryonic fibroblasts
Project description:GCN2 (General Control Nonderepressible 2) is a serine/threonine-protein kinase that controls mRNA translation in response to amino acid availability. Here we show that production and clearance of erythrocytes are controlled by GCN2. Our data highlight the importance of tissue-resident macrophages as the primary cell type mediating this effect. During different stress conditions, such as hemolysis, amino acid deficiency or hypoxia, GCN2 knockout (GCN2-/-) mice displayed resistance to anemia as compared to wild-type (GCN2+/+) mice. GCN2-/- liver macrophages display defective erythrophagocytosis and lysosome maturation. Molecular analysis of GCN2-/- cells indicates that the ATF4-NRF2 pathway is a critical downstream mediator of GCN2 in regulating RBC clearance and iron recycling. We performed NRF2 (Nfe2l2) ChIP-seq experiments in both WT and GCN2 KO MEFs with or without leucine deprivation.
Project description:Besides being building blocks for protein synthesis, amino acids serve a wide variety of cellular functions, including acting as metabolic intermediates for ATP generation and for redox homeostasis. Upon amino acid deprivation, free uncharged tRNAs trigger GCN2-ATF4 to mediate the well-characterized transcriptional amino acid response (AAR). However, it is not clear whether the deprivation of different individual amino acids triggers identical or distinct AARs. Here, we characterized the global transcriptional response upon deprivation of one amino acid at a time. With the exception of glycine, which was not required for the proliferation of MCF7 cells, we found that the deprivation of most amino acids triggered a shared transcriptional response that included the activation of ATF4, p53 and TXNIP. However, there was also significant heterogeneity among different individual AARs. The most dramatic transcriptional response was triggered by methionine deprivation, which activated an extensive and unique response in different cell types. We uncovered that the specific methionine-deprived transcriptional response required creatine biosynthesis. This dependency on creatine biosynthesis was caused by the consumption of S-Adenosyl-L-methionine (SAM) during creatine biosynthesis that helps to deplete SAM under methionine deprivation and reduces histone methylations. As such, the simultaneous deprivation of methionine and sources of creatine biosynthesis (either arginine or glycine) abolished the reduction of histone methylation and the methionine-specific transcriptional response. Arginine-derived ornithine was also required for the complete induction of the methionine-deprived specific gene response. Collectively, our data identify a previously unknown set of heterogeneous amino acid responses and reveal a distinct methionine-deprived transcriptional response that results from the crosstalk of arginine, glycine and methionine metabolism via arginine/glycine-dependent creatine biosynthesis.