Obesity challenges the hepatoprotective function of the integrated stress response to asparaginase exposure in mice

J Biol Chem. 2017 Apr 21;292(16):6786-6798. doi: 10.1074/jbc.M116.768408. Epub 2017 Feb 27.

Abstract

Obesity increases risk for liver toxicity by the anti-leukemic agent asparaginase, but the mechanism is unknown. Asparaginase activates the integrated stress response (ISR) via sensing amino acid depletion by the eukaryotic initiation factor 2 (eIF2) kinase GCN2. The goal of this work was to discern the impact of obesity, alone versus alongside genetic disruption of the ISR, on mechanisms of liver protection during chronic asparaginase exposure in mice. Following diet-induced obesity, biochemical analysis of livers revealed that asparaginase provoked hepatic steatosis that coincided with activation of another eIF2 kinase PKR-like endoplasmic reticulum kinase (PERK), a major ISR transducer to ER stress. Genetic loss of Gcn2 intensified hepatic PERK activation to asparaginase, yet surprisingly, mRNA levels of key ISR gene targets such as Atf5 and Trib3 failed to increase. Instead, mechanistic target of rapamycin complex 1 (mTORC1) signal transduction was unleashed, and this coincided with liver dysfunction reflected by a failure to maintain hydrogen sulfide production or apolipoprotein B100 (ApoB100) expression. In contrast, obese mice lacking hepatic activating transcription factor 4 (Atf4) showed an exaggerated ISR and greater loss of endogenous hydrogen sulfide but normal inhibition of mTORC1 and maintenance of ApoB100 during asparaginase exposure. In both genetic mouse models, expression and phosphorylation of Sestrin2, an ATF4 gene target, was increased by asparaginase, suggesting mTORC1 inhibition during asparaginase exposure is not driven via eIF2-ATF4-Sestrin2. In conclusion, obesity promotes a maladaptive ISR during asparaginase exposure. GCN2 functions to repress mTORC1 activity and maintain ApoB100 protein levels independently of Atf4 expression, whereas hydrogen sulfide production is promoted via GCN2-ATF4 pathway.

Keywords: PKR-like endoplasmic reticulum kinase (PERK); activating transcription factor 4 (ATF4); eukaryotic initiation factor 2 (eIF2); general control nonderepressible 2 (GCN2); hydrogen sulfide; integrated stress response; liver; mammalian target of rapamycin (mTOR); obesity; sestrin2.

MeSH terms

  • Activating Transcription Factor 4 / genetics
  • Activating Transcription Factors / metabolism
  • Animals
  • Apolipoprotein B-100 / metabolism
  • Asparaginase / metabolism*
  • Cell Cycle Proteins / metabolism
  • Disease Models, Animal
  • Eukaryotic Initiation Factor-2 / metabolism
  • Fatty Liver / metabolism*
  • Fatty Liver / pathology
  • Gene Deletion
  • Glutathione / chemistry
  • Hydrogen Sulfide / chemistry
  • Liver / drug effects
  • Liver / metabolism
  • Liver / pathology*
  • Mechanistic Target of Rapamycin Complex 1
  • Mice
  • Mice, Inbred C57BL
  • Mice, Obese
  • Mice, Transgenic
  • Multiprotein Complexes / metabolism
  • Nuclear Proteins / genetics
  • Obesity / metabolism*
  • Peroxidases
  • Protein-Serine-Threonine Kinases / genetics
  • TOR Serine-Threonine Kinases / metabolism
  • eIF-2 Kinase / metabolism

Substances

  • Activating Transcription Factors
  • Apolipoprotein B-100
  • Atf4 protein, mouse
  • Atf5 protein, mouse
  • Cell Cycle Proteins
  • Eukaryotic Initiation Factor-2
  • Multiprotein Complexes
  • Nuclear Proteins
  • TRB3 protein, mouse
  • Activating Transcription Factor 4
  • Peroxidases
  • sestrin 2 protein, mouse
  • TOR Serine-Threonine Kinases
  • Eif2ak4 protein, mouse
  • Mechanistic Target of Rapamycin Complex 1
  • PERK kinase
  • Protein-Serine-Threonine Kinases
  • eIF-2 Kinase
  • Asparaginase
  • Glutathione
  • Hydrogen Sulfide