The GCN2 eIF2α Kinase Is Required for Adaptation to Amino Acid Deprivation in Mice

Abstract

The GCN2 eIF2␣ kinase is essential for activation of the general amino acid control pathway in yeast when one or more amino acids become limiting for growth. GCN2's function in mammals is unknown, but must differ, since mammals, unlike yeast, can synthesize only half of the standard 20 amino acids. To investigate the function of mammalian GCN2, we have generated a Gcn2 ؊/؊ knockout strain of mice. Gcn2 ؊/؊ mice are viable, fertile, and exhibit no phenotypic abnormalities under standard growth conditions. However, prenatal and neonatal mortalities are significantly increased in Gcn2 ؊/؊ mice whose mothers were reared on leucine-, tryptophan-, or glycine-deficient diets during gestation. Leucine deprivation produced the most pronounced effect, with a 63% reduction in the expected number of viable neonatal mice. Cultured embryonic stem cells derived from Gcn2 ؊/؊ mice failed to show the normal induction of eIF2␣ phosphorylation in cells deprived of leucine. To assess the biochemical effects of the loss of GCN2 in the whole animal, liver perfusion experiments were conducted. Histidine limitation in the presence of histidinol induced a twofold increase in the phosphorylation of eIF2␣ and a concomitant reduction in eIF2B activity in perfused livers from wild-type mice, but no changes in livers from Gcn2 ؊/؊ mice.

Upregulation of tryptophanyl-tRNA synthethase adapts human cancer cells to nutritional stress caused by tryptophan degradation

“…As ATF4 has been reported to regulate the transcription of many tRNA synthetases 25,30–32 , we next compared the expression of WARS to that of all other tRNA synthetases in U87-MG glioblastoma cells that were Trp starved for 24 h. Trp starvation most strongly induced WARS mRNA expression (2,6 fold; Figure 4O). In addition, 7 other tRNA synthetases (glycyl-tRNA synthetase, GARS; cysteinyl-tRNA synthetase, CARS; alanyl-tRNA synthetase, AARS; methionyl-tRNA synthetase, MARS; seryl-tRNA synthetase, SARS; tyrosyl-tRNA synthetase, YARS and glutamyl-prolyl-tRNA synthetase, EPRS) were upregulated more than 1.5 fold.…”

“…GCN2 is activated by sensing of uncharged tRNA and therefore should not be specific for Trp starvation 25,26 . In keeping with this, depletion of any essential amino acid resulted in an induction of WARS mRNA, albeit to different levels with depletion of Trp, valine and phenylalanine being the strongest inducers of WARS (Figure 4I).…”

Dynamics of unfolded protein response in recombinant CHO cells

“…For example, the PERK pathway has been shown to be activated by glucose deprivation and under hypoxic conditions (Koumenis et al 2002;Elanchezhian et al 2012). Similarly, amino-acid limitation also leads to attenuation of protein synthesis by phosphorylation of EIF2a phosphorylation via GCN2 kinase (Zhang et al 2002). Studies have also shown upregulation of CHOP in response to glucose and glutamine deprivation in both CHO and NSO cell lines (Murphy et al 2001;Lengwehasatit and Dickson 2002).…”

Reversible induction of translational isoforms of p53 in glucose deprivation

“…21,22 Amino acid depletion induces GCN2 kinase-mediated phosphorylation of eIF2α, leading to a global decrease in protein synthesis and induction of an adaptive survival program. 21,23 Under this condition, IRES-mediated translation of the Cat-1 and SNAT2 …”

“…21,22 Amino acid depletion induces GCN2 kinase-mediated phosphorylation of eIF2α, leading to a global decrease in protein synthesis and induction of an adaptive survival program. 21,23 Under this condition, IRES-mediated translation of the Cat-1 and SNAT2 mRNAs occur, 24,25 thus preparing cells to transport amino acids once they become available. Methionine synthase, a key enzyme that clears intracellular homocysteine, is induced by its cofactor, vitamin B12, at a translational level through an IRES in the 5'UTR of the mRNA.…”