The eIF2 Kinase GCN2 Is Essential for the Murine Immune System to Adapt to Amino Acid Deprivation by Asparaginase

Abstract

Amino acid starvation by asparaginase (ASNase) enhances phosphorylation of eukaryotic initiation factor 2 (eIF2) by general control nonderepressible 2 (GCN2) kinase, leading to reduced global mRNA translation rates. This conserves energy and allows cells time to reprogram stress-related gene expression to alleviate cell injury. This study addressed the importance of GCN2 for the immune system to adapt to amino acid starvation by ASNase. GCN2(+/+) and GCN2(-/-) mice were injected once daily with ASNase or saline for up to 7 d. In both thymus and spleen, activation of amino acid stress response genes to ASNase, such as asparagine synthetase and CAAT enhancer binding protein homologous protein, required GCN2. ASNase reduced food intake and body weight in both genotypes, but spleen and thymus wet weights and total cell numbers in thymus, spleen, bone marrow, and mesenteric lymph nodes were less in GCN2(-/-) mice treated with ASNase (genotype x ASNase, P < 0.05). In the thymus, GCN2(-/-) mice treated with ASNase demonstrated enhanced apoptosis and fewer cells in all subpopulations examined (CD3+, CD4-8-, CD4+8+, CD4+8-, CD4-8+) compared with GCN2(+/+) mice treated with ASNase (genotype x ASNase, P < 0.05). In the spleen, GCN2 deletion magnified ASNase-induced reductions in CD4+ T cells, CD8+ T cells, CD19+ B cells, and CD11b+ leukocytes (genotype x ASNase, P < 0.05). These results indicate that loss of GCN2 enhances immunosuppression by ASNase and that this eIF2 kinase is broadly required for amino acid stress management in the immune system.

General control nonderepressible 2 deletion predisposes to asparaginase-associated pancreatitis in mice

“…Activation of the AAR by GCN2 is essential for adaptation and survival during asparaginase treatment. In the absence of GCN2, failure to induce the AAR augments immunosuppression (8) and hepatotoxicity (64,65). These disease outcomes are in agreement with human genetic studies that report a correlation between single-nucleotide polymorphisms (SNPs) in the AAR genes asparagine synthetase (ASNS) and ATF5 and worse treatment outcome to asparaginase (6,49).…”

GCN2 is required to increase fibroblast growth factor 21 and maintain hepatic triglyceride homeostasis during asparaginase treatment

“…L-Asparaginase is an antileukemic agent that depletes circulating levels of asparagine. The activity of asparaginase derived from Escherichia coli (Elspar; Merck) was determined by the Nesslerization technique, as previously described (11,43). Briefly, the production of ammonia by asparaginase over time was measured and compared with known ammonia standards.…”

General Control Nonderepressible 2 (GCN2) Kinase Protects Oligodendrocytes and White Matter during Branched-chain Amino Acid Deficiency in Mice

“…ATF4 directly enhances the transcriptional expression of genes involved in the synthesis, transport, and metabolism of amino acids and boosts antioxidant defense capacity, providing cells the means to restore a healthy state (5). Studies of Gcn2 null (Gcn2 Ϫ/Ϫ ) mice demonstrate essential roles of the GCN2-mediated AAR in food selection, growth, and survival (6 -9), hepatic lipid metabolism (10), and immune function (11,12). Additionally, GCN2 facilitates the ability of single amino acid deprivation to mediate resistance to ischemic damage in renal and liver tissues elicited by surgical reperfusion in mice (13).…”