Project description:In response to different cellular stressors, the ISR kinases, PERK, PKR, HRI and GCN2, activate downstream transcriptional programs. While the core ISR transcription program is well characterized, markers that are specific to each individual ISR kinase activation pathway are not known. To identify markers that are induced by PERK or GCN2, but not the other ISR kinases, we subjected WT, GCN2-/-, and PERK-/- MEFs to amino acid starvation (RPMI 1640 SILAC -Lys -Arg) or Thapsigargin (200nM) treatment for 6 hours to activate the GCN2 and PERK pathways, respectively and performed RNA sequencing.
Project description:Diverse environmental insults induce the integrated stress response (ISR), which features eIF2 phosphorylation and translational control that serves to restore protein homeostasis. The eIF2 kinase GCN2 is a first responder in the ISR that is activated by amino acid depletion and other unrelated stresses. Two processes are suggested to trigger an ordered process of GCN2 activation during stress: GCN2 monitoring stress via accumulating uncharged tRNAs or by stalled and colliding ribosomes. Our results suggest that while ribosomal collisions are indeed essential for GCN2 activation in response to translational elongation inhibitors, conditions that trigger deacylation of tRNAs activate GCN2 via its direct association with affected tRNAs. Both process require the GCN2 regulatory domain related to histidyl tRNA synthetases. GCN2 activation by UV irradiation features lowered amino acids and increased uncharged tRNAs and ribosome collisions are dispensable. We conclude that there are multiple mechanisms that activate GCN2 during diverse stresses.
Project description:Ribosome stalling during translation has recently been shown to cause neurodegeneration, yet the signaling pathways triggered by stalled elongation complexes are unknown. To investigate these pathways we analyzed the brain of B6J-nmf205-/- mice in which neuronal elongation complexes are stalled at AGA codons due to deficiencies in a tRNA Arg(UCU) tRNA and GTPBP2, a mammalian ribosome rescue factor. Increased levels of phosphorylation of eIF2α (Ser51) were detected prior to neurodegeneration in these mice and transcriptome analysis demonstrated activation of ATF4, a key transcription factor in the integrated stress response (ISR) pathway. Genetic experiments showed that this pathway was activated by the eIF2alpha kinase, GCN2, in an apparent deacylated tRNA-independent fashion. Further we found that the ISR attenuates neurodegeneration in B6J-nmf205-/- mice, underscoring the importance of cellular and stress context on the outcome of activation of this pathway. These results demonstrate the critical interplay between translation elongation and initiation in regulating neuron survival during cellular stress. Examination of gene expression in cerebellum and hippocampus for 4 mice strains derived from C57BL/6J (B6J) strain. Microarray data was performed for 3 week and 5 week old mice in both cerebellum and hippocampus for B6J and B6J-nmf205-/- three replicates each. RNA-Seq data was perform on cerebellum of mice 3 weeks old, three replicates for each genotype: B6J, B6J-nmf205-/-, B6J-Gcn2-/- and B6J-nmf205-/-;Gcn2-/-.
Project description:Ribosome stalling during translation has recently been shown to cause neurodegeneration, yet the signaling pathways triggered by stalled elongation complexes are unknown. To investigate these pathways we analyzed the brain of B6J-nmf205-/- mice in which neuronal elongation complexes are stalled at AGA codons due to deficiencies in a tRNA Arg(UCU) tRNA and GTPBP2, a mammalian ribosome rescue factor. Increased levels of phosphorylation of eIF2α (Ser51) were detected prior to neurodegeneration in these mice and transcriptome analysis demonstrated activation of ATF4, a key transcription factor in the integrated stress response (ISR) pathway. Genetic experiments showed that this pathway was activated by the eIF2α kinase, GCN2, in an apparent deacylated tRNA-independent fashion. Further we found that the ISR attenuates neurodegeneration in B6J-nmf205-/- mice, underscoring the importance of cellular and stress context on the outcome of activation of this pathway. These results demonstrate the critical interplay between translation elongation and initiation in regulating neuron survival during cellular stress. Examination of gene expression in cerebellum and hippocampus for 4 mice strains derived from C57BL/6J (B6J) strain. Microarray data was performed for 3 week and 5 week old mice in both cerebellum and hippocampus for B6J and B6J-nmf205-/- three replicates each. RNA-Seq data was perform on cerebellum of mice 3 weeks old, three replicates for each genotype: B6J, B6J-nmf205-/-, B6J-Gcn2-/- and B6J-nmf205-/-;Gcn2-/-.
Project description:Ribosome stalling occurring on aberrant mRNA activates quality control pathways to maintain proteostasis. Recently, ribosome stalling has also been linked to the activation of Gcn2 and the subsequent integrated-stress response (ISR). How the two processes are coordinated is not completely clear. Here we show that activation of ribosome-quality control by Hel2 suppresses that of Gcn2 in yeast. In the absence of Hel2, we observe a gene-expression signature indicative of ISR activation, suggesting that factor is used to suppress premature activation of Gcn2 in the absence of stress conditions. We further show that Hel2 and Gcn2 are activated by similar set of agents that cause ribosome stalling, with Hel2’s maximal activation occurring at lower frequency of stalling. Interestingly, inactivation of one pathway was found to result in the overactivation of the other, suggesting that both are activated by the same signal. Indeed, we provide evidence that suggests that, similar to Hel2, Gcn2 is activated by ribosome collisions. Collectively, our findings provide interesting details about how the multiple pathways that recognize stalled ribosomes coordinate to mount the appropriate response.
Project description:To determine transcriptome changes in adult spinal cord induced by the combined effect of having the GarsP278KY mutation while lacking GCN2 kinase . How mutations in broadly expressed housekeeping genes lead to neurodegeneration in specific cell types remains unclear. Mutations in ubiquitously expressed tRNA synthetase genes cause axonal peripheral neuropathy, accounting for at least six forms of Charcot-Marie-Tooth disease. Genetic evidence in mouse and Drosophila models suggests a neomorphic gain-of-function mechanism. Here, we use in vivo, cell-type-specific transcriptional and translational profiling of affected peripheral neurons to show that mutant tRNA synthetases impair translation and activate the integrated stress response (ISR) through the sensor kinase, GCN2. The chronic activation of the ISR contributes to the pathophysiology, and genetic deletion of Gcn2 alleviates the peripheral neuropathy. The activation of GCN2 by tRNA synthetase mutations indicates their neomorphic activity is still related to translation and suggests inhibiting GCN2 or the ISR as a therapeutic strategy.
Project description:To identify the target genes of integrated stress reponse (ISR), we have employed whole genome microarray expression in MEF cells. ISR gene setimation under ER stress condition using Perk -/-, Atf4 -/-, eIF2a S51A mutant, Fv2E-PERK MEF cells
Project description:To determine transcriptome changes in spinal cord induced by the GarsdelETAQ mutation. How mutations in broadly expressed housekeeping genes lead to neurodegeneration in specific cell types remains unclear. Mutations in ubiquitously expressed tRNA synthetase genes cause axonal peripheral neuropathy, accounting for at least six forms of Charcot-Marie-Tooth disease. Genetic evidence in mouse and Drosophila models suggests a neomorphic gain-of-function mechanism. Here, we use in vivo, cell-type-specific transcriptional and translational profiling of affected peripheral neurons to show that mutant tRNA synthetases impair translation and activate the integrated stress response (ISR) through the sensor kinase, GCN2. The chronic activation of the ISR contributes to the pathophysiology, and genetic deletion of Gcn2 alleviates the peripheral neuropathy. The activation of GCN2 by tRNA synthetase mutations indicates their neomorphic activity is still related to translation and suggests inhibiting GCN2 or the ISR as a therapeutic strategy.