The eukaryotic initiation factor 2 kinase GCN2 protects against hepatotoxicity during asparaginase treatment

Abstract

Asparaginase is an important drug in the treatment regimen for acute lymphoblastic leukemia. Asparaginase depletes circulating asparagine and glutamine, activating an amino acid stress response (AAR) involving phosphorylation of eukaryotic initiation factor 2 (eIF2) by general control nonderepressible kinase 2 (GCN2). We hypothesized that GCN2 functions to mitigate hepatic stress during asparaginase therapy by activating the AAR. To test this idea, C57BL/6J wild-type mice (Gcn2(+/+)) and those deleted for Gcn2 (Gcn2(-/-)) were injected with asparaginase or saline excipient one time daily for 1 or 6 days. In liver, increased phosphorylation of eIF2 and mRNA expression of AAR target genes activating transcription factor 4, asparagine synthetase, eIF4E-binding protein 1, and CAAT enhancer-binding protein homologous protein were significantly blunted or blocked in the liver of Gcn2(-/-) mice. Loss of AAR during asparaginase coincided with increases in mammalian target of rapamycin signaling, hepatic triglyceride accumulation, and DNA damage in association with genetic markers of oxidative stress (glutathione peroxidase) and inflammation (tumor necrosis factor alpha-α). Although asparaginase depleted circulating asparagine in both Gcn2(+/+) and Gcn2(-/-) mice, all other amino acids, including plasma glutamine, were elevated in the plasma of Gcn2(-/-) mice. This study shows that loss of GCN2 promotes oxidative stress and inflammatory-mediated DNA damage during asparaginase therapy, suggesting that patients with reduced or dysfunctional AAR may be at risk of developing hepatic complications during asparaginase treatment.

Time-resolved analysis of amino acid stress identifies eIF2 phosphorylation as necessary to inhibit mTORC1 activity in liver

“…This suppressive role of GCN2 was first observed by us in mice fed a leucine devoid diet to Gcn2 -/-mice (10), then confirmed and further detailed using mice treated with asparaginase (8,9,19,25). This work also strongly supports the findings of Averous et al who used a model of leucine deprivation in mouse embryonic fibroblasts (MEFs) (20) to conclude that GCN2 and eIF2 phosphorylation, but not ATF4, are required for continuous suppression of mTORC1 during leucine or arginine deprivation.…”

“…Notably, asparagine concentrations were consistently reduced over time whereas glutamine concentrations were acutely reduced at 3 h post injection which then recovered to serum levels in untreated mice by 12 h ( Figure S1). Circulating levels of most other amino acids and in particular the dietary essential amino acids steadily increased over 24 h ( Figure S2) (9). Activation states of GCN2 and mTORC1 were tracked by assessing phosphorylation of their respective substrates, eIF2 and S6K1, respectively.…”

“…Inappropriate activation of mTORC1 during cytoplasmic or proteotoxic stress has deleterious effects for both cells (7) and organisms (8)(9)(10)(11)(12). Our lab was the first to identify the existence of coordinated crosstalk between the ISR and mTORC1 pathway in mammals following amino acid deprivation (10).…”

Mitomycin-Induced Pulmonary Veno-Occlusive Disease

“…4 According to our results, we can hypothesize that MMC depletes GCN2 in the lungs and mimics PVOD induced by EIF2AK4 mutations. Interestingly, Wilson et al 37 have demonstrated that the loss of GCN2 promotes oxidative stress and inflammatory-mediated DNA damage during asparaginase therapy; this suggests that patients with reduced GCN2 may be at risk of developing hepatic complications during asparaginase treatment. Our results may suggest that MMC-induced GCN2 depletion could favor similar oxidative and inflammatory pulmonary injuries.…”

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

“…Previous reports from our laboratory and others demonstrate that mice deleted for Gcn2 fail to phosphorylate eIF2 during both dietary and pharmaceutical amino acid deprivation, resulting in hepatic steatosis and liver injury (2,12,24,43,50). Depletion of circulating asparagine and glutamine is accomplished by asparaginase (37,39), an effective tumor killing agent in patients diagnosed with acute lymphoblastic leukemia.…”