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Obesity intensifies hepatotoxicity by asparaginase in mice deleted for GCN2 but not ATF4
Author(s) -
Nikonorova Inna A.,
Mirek Emily T.,
Wang Yongping,
Dixon Joseph L.,
Anthony Tracy G.
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1126.1
Subject(s) - atf4 , integrated stress response , glutamine , medicine , endocrinology , unfolded protein response , asparagine synthetase , argininosuccinate synthase , biology , amino acid , biochemistry , apoptosis , messenger rna , translation (biology) , gene , arginine , arginase
Liver dysfunction is a serious adverse effect of asparaginase treatment in patients with acute lymphoblastic leukemia, reducing overall survival. Asparaginase depletes asparagine and glutamine levels in the blood causing rapid tumor regression. Depletion of these amino acids also reduces liver protein synthesis via phosphorylation of eukaryotic initiation factor 2 (eIF2) by the GCN2 (aka eIF2AK4) kinase. Phosphorylation of eIF2 promotes synthesis of activating transcription factor 4 (ATF4) which reconfigures the cellular transcriptome to alleviate the amino acid stress. Failure of this integrated stress response (ISR) leads to severe liver dysfunction. A potent clinical predictor of hepatotoxicity by asparaginase is pre‐existing obesity. Molecular mechanisms of this clinical observation remain to be determined. The focus of our study was to examine the role of the ISR pathway on the background of obesity in the development of hepatotoxicity by asparaginase. Wild type, Gcn2 − / − and liver specific‐Atf4 −/− ( ls‐Atf4 − / − ) mice of C57Bl/6J background were fed a high fat diet for 12 weeks. The onset of obesity was monitored by assessing body composition and glucose metabolism. Mice were randomly assigned to receive daily injections of Elspar L‐asparaginase at 0 or 3 IU per gram body weight for 8 days. Liver tissues were collected and analyzed by immunoblotting for activation of the ISR pathway and its crosstalk to usual suspects of liver dysfunction, mTORC1 and unfolded protein response (UPR) pathways. Our data showed that asparaginase treatment of obese mice resulted in hepatic steatosis that intensified significantly in Gcn2 − / − but not ls‐Atf4 − / − mice. Liver pathology in Gcn2 − / − mice corresponded with induction of the UPR pathway that was assessed by PERK (aka eIF2AK3) phosphorylation. PERK phosphorylation was moderate in the livers of asparaginase‐treated wild type and ls‐ATF4 − / − mice (5‐fold) and very intense in the livers of Gcn2 − / − mice (20‐fold). Asparaginase treatment corresponded with reduced mTORC1 activity (3‐fold reduction in p70S6K phosphorylation and 2‐fold reduction in 4EBP1 phosphorylation) in wild type and ls‐Atf4 − / − livers, whereas Gcn2 − / − group demonstrated strong activation of mTORC1 pathway (2‐fold increase in mTOR‐Ser2448 and 4EBP1 phosphorylation, 3‐fold increase in p70S6K phosphorylation). Downregulation of mTORC1 pathway in the livers of asparaginase‐treated wild type mice and the absence of such downregulation in asparaginase‐treated Gcn2 − / − mice suggest that GCN2 signals to mTORC1 pathway. Furthermore, downregulation of mTORC1 in asparaginase‐treated ls‐Atf4 − / − livers suggest that the point of coordination of GCN2 pathway to mTORC1 pathway is not through ATF4. Overall our study provides important molecular insights into the mechanism of acute liver damage by asparaginase and identifies a novel role for the ISR in coordinating mTORC1 signal transduction. Support or Funding Information NIH HD070487