Browsing by Author "Cundiff, Judy K."

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    THE EIF2 KINASE PERK AND THE INTEGRATED STRESS RESPONSE FACILITATE ACTIVATION OF ATF6 DURING ENDOPLASMIC RETICULUM STRESS
    (Office of the Vice Chancellor for Research, 2012-04-13) Teske, Brian F.; Wek, Ronald C.; Wek, Sheree A.; Bunpo, Piyawan; Cundiff, Judy K.; McClintick, Jeanette N.; Anthony, Tracy G.; Wek, Ronald C.
    Disruptions of the endoplasmic reticulum (ER) that perturb protein folding cause ER stress and elicit an unfolded protein response (UPR) that involves changes in gene expression aimed at expanding the ER protein processing capacity and alleviating cellular injury. Three ER stress sensors PERK, ATF6, and IRE1 implement the UPR. Mutations of these ER stress sensors have been linked to diabetes, cancer and neurodegenerative diseases. Consequently, understanding the regulation of these three pathways has substantial therapeutic potential for development of biomarkers and pharmaceuticals for management of these conditions. PERK phosphorylation of eIF2 during ER stress represses protein synthesis, which prevents further influx of ER client proteins. PERK phosphorylation of eIF2 (eIF2~P) also induces preferential translation of ATF4, a transcription activator of the UPR. In this study we show that the PERK/eIF2~P/ATF4 pathway is required not only for translational control, but also activation of ATF6 and its target genes. The PERK pathway facilitates both the synthesis of ATF6 and trafficking of ATF6 from the ER to the Golgi for intramembrane proteolysis and activation of ATF6. As a consequence, liver-specific depletion of PERK significantly reduces both the translational and transcriptional phases of the UPR, leading to reduced protein chaperone expression, disruptions of lipid metabolism, and enhanced apoptosis. These findings show that the regulatory networks of the UPR are fully integrated, and helps explain the diverse biological defects associated with loss of PERK.
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    The eukaryotic initiation factor 2 kinase GCN2 protects against hepatotoxicity during asparaginase treatment
    (American Physiological Society, 2013-11) Wilson, Gabriel J.; Bunpo, Piyawan; Cundiff, Judy K.; Wek, Ronald C.; Anthony, Tracy G.; Biochemistry & Molecular Biology, School of Medicine
    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.
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    General Control Nonderepressible 2 (GCN2) Kinase Protects Oligodendrocytes and White Matter during Branched-Chain Amino Acid Deficiency in Mice
    (2013-09) She, Pengxiang; Bunpo, Piyawan; Cundiff, Judy K.; Wek, Ronald C.; Harris, Robert A.; Anthony, Tracy G.; Department of Biochemistry and Molecular Biology, IU School of Medicine
    Branched-chain amino acid (BCAA) catabolism is regulated by branched-chain α-keto acid dehydrogenase, an enzyme complex that is inhibited when phosphorylated by its kinase (BDK). Loss of BDK function in mice and humans causes BCAA deficiency and epilepsy with autistic features. In response to amino acid deficiency, phosphorylation of eukaryotic initiation factor 2α (eIF2∼P) by general control nonderepressible 2 (GCN2) activates the amino acid stress response. We hypothesized that GCN2 functions to protect the brain during chronic BCAA deficiency. To test this idea, we generated mice lacking both Gcn2 and Bdk (GBDK) and examined the development of progeny. GBDK mice appeared normal at birth, but they soon stopped growing, developed severe ataxia, tremor, and anorexia, and died by postnatal day 15. BCAA levels in brain were diminished in both Bdk−/− and GBDK pups. Brains from Bdk−/− pups exhibited robust eIF2∼P and amino acid stress response induction, whereas these responses were absent in GBDK mouse brains. Instead, myelin deficiency and diminished expression of myelin basic protein were noted in GBDK brains. Genetic markers of oligodendrocytes and astrocytes were also reduced in GBDK brains in association with apoptotic cell death in white matter regions of the brain. GBDK brains further demonstrated reduced Sod2 and Cat mRNA and increased Tnfα mRNA expression. The data are consistent with the idea that loss of GCN2 during BCAA deficiency compromises glial cell defenses to oxidative and inflammatory stress. We conclude that GCN2 protects the brain from developing a lethal leukodystrophy in response to amino acid deficiencies.