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

• Published in: The Journal of biological chemistry Vol. 292; no. 16; pp. 6786 - 6798
• Main Authors: Nikonorova, Inna A., Al-Baghdadi, Rana J.T., Mirek, Emily T., Wang, Yongping, Goudie, Michael P., Wetstein, Berish B., Dixon, Joseph L., Hine, Christopher, Mitchell, James R., Adams, Christopher M., Wek, Ronald C., Anthony, Tracy G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 21.04.2017; American Society for Biochemistry and Molecular Biology
• Subjects: activating transcription factor 4 (ATF4); Activating Transcription Factor 4 - genetics; Activating Transcription Factors - metabolism; Animals; Apolipoprotein B-100 - metabolism; Asparaginase - metabolism; Cell Cycle Proteins - metabolism; Disease Models, Animal; eIF-2 Kinase - metabolism; eukaryotic initiation factor 2 (eIF2); Eukaryotic Initiation Factor-2 - metabolism; Fatty Liver - metabolism; Fatty Liver - pathology; Gene Deletion; general control nonderepressible 2 (GCN2); Glutathione - chemistry; hydrogen sulfide; Hydrogen Sulfide - chemistry; integrated stress response; liver; Liver - drug effects; Liver - metabolism; Liver - pathology; mammalian target of rapamycin (mTOR); Mechanistic Target of Rapamycin Complex 1; Mice; Mice, Inbred C57BL; Mice, Obese; Mice, Transgenic; Molecular Bases of Disease; Multiprotein Complexes - metabolism; Nuclear Proteins - genetics; obesity; Obesity - metabolism; Peroxidases; PKR-like endoplasmic reticulum kinase (PERK); Protein-Serine-Threonine Kinases - genetics; sestrin2; TOR Serine-Threonine Kinases - metabolism; general control nonderepressible 2 (GCN2); hydrogen sulfide; liver; PKR-like endoplasmic reticulum kinase (PERK); eukaryotic initiation factor 2 (eIF2); mammalian target of rapamycin (mTOR); activating transcription factor 4 (ATF4); obesity; integrated stress response; sestrin2
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M116.768408

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.