Essential Role of PACT-Mediated PKR Activation in Tunicamycin-Induced Apoptosis

Singh, Madhurima; Fowlkes, Vennece; Handy, Indhira; Patel, Chandrashekhar V.; Patel, Rekha C.

doi:10.1016/j.jmb.2008.10.068

Cited by 43 publications

(53 citation statements)

References 79 publications

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“…Our data suggest that hyperoxia-induced, PKR-mediated CHOP induction may be the mechanism by which hyperoxia augments cell death during ER stress. This is supported by the recent report that PKR activation by its endogenous activator PACT is required for maximal CHOP induction and cell death following tunicamycin-induced ER stress (36). We speculate that PKR activation and CHOP induction during O 2 therapy or in response to viral activation may promote further lung injury in diseases associated with epithelial ER stress, such as idiopathic pulmonary fibrosis (18,19) and smoking-related lung disease (14,16,17,22).…”

Section: Discussionsupporting

confidence: 70%

PKR-dependent CHOP induction limits hyperoxia-induced lung injury

Lozon¹,

Eastman²,

Matute-Bello

et al. 2011

American Journal of Physiology-Lung Cellular and Molecular Phys

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Lozon TI, Eastman AJ, Matute-Bello G, Chen P, Hallstrand TS, Altemeier WA. PKR-dependent CHOP induction limits hyperoxia-induced lung injury. Am J Physiol Lung Cell Mol Physiol 300: L422-L429, 2011. First published December 24, 2010 doi:10.1152 doi:10. /ajplung.00166.2010 is commonly employed in patients with respiratory failure; however, hyperoxia is also a potential contributor to lung injury. In animal models, hyperoxia causes oxidative stress in the lungs, resulting in increased inflammation, edema, and permeability. We hypothesized that oxidative stress from prolonged hyperoxia leads to endoplasmic reticulum (ER) stress, resulting in activation of the unfolded protein response (UPR) and induction of CCAAT enhancer-binding protein homologous protein (CHOP), a transcription factor associated with cell death in the setting of persistent ER stress. To test this hypothesis, we exposed the mouse lung epithelial cell line MLE-12 to 95% O2 for 8 -24 h and evaluated for evidence of UPR induction and CHOP induction. Hyperoxia caused increased CHOP expression without other evidence of UPR activation. Because CHOP expression is preceded by phosphorylation of the ␣-subunit of the eukaryotic initiation factor-2 (eIF2␣), we evaluated the role of double-stranded RNA-activated protein kinase (PKR), a non-UPR-associated eIF2␣ kinase. Hyperoxia caused PKR phosphorylation, and RNA interference knockdown of PKR attenuated hyperoxia-induced CHOP expression. In vivo, hyperoxia induced PKR phosphorylation and CHOP expression in the lungs without other biochemical evidence for ER stress. Additionally, Ddit3 Ϫ/Ϫ (CHOP-null) mice had increased lung edema and permeability, indicating a previously unknown protective role for CHOP after prolonged hyperoxia. We conclude that hyperoxia increases CHOP expression via an ER stress-independent, PKRdependent pathway and that increased CHOP expression protects against hyperoxia-induced lung injury.CCAAT enhancer-binding protein homologous protein; acute respiratory distress syndrome; endoplasmic reticulum stress; epithelial cell; eukaryotic initiation factor-2␣; activating transcription factor-4; double-stranded RNA-activated protein kinase OXYGEN SUPPLEMENTATION is routinely used in the management of patients with acute respiratory failure. However, prolonged exposure to hyperoxia has long been recognized as a potential contributor to acute lung injury (26). In animals, prolonged exposure to hyperoxia causes lung injury, characterized by cell death, increased lung permeability, edema, and inflammation (5, 29). Although the exact mechanisms by which hyperoxia causes lung injury are incompletely understood, generation of reactive oxygen species (ROS) and cellular apoptosis appear to play important roles (1).One potential mechanism linking ROS generation and cell death is endoplasmic reticulum (ER) stress, resulting in activation of the associated unfolded protein response (UPR) (23). The ER functions to modify proteins for subsequent exposure to the extracellular environment. ER stress occurs ...

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Section: Discussionsupporting

confidence: 70%

PKR-dependent CHOP induction limits hyperoxia-induced lung injury

Lozon¹,

Eastman²,

Matute-Bello

et al. 2011

American Journal of Physiology-Lung Cellular and Molecular Phys

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“…PKR, an eIF2α kinase, has recently emerged to be involved in ER stress-induced apoptosis by pharmacological ER inducers, thapsigargine and tunicamycin [20,31,32]. Lee et al found that activated PKR phosphorylated the eIF2α in a PERK-independent manner when HEK293A cells were treated with thapsigargine [20].…”

Section: Discussionmentioning

confidence: 99%

Signaling dynamics of palmitate-induced ER stress responses mediated by ATF4 in HepG2 cells

Cho¹,

Wu²,

Zhang³

et al. 2013

BMC Syst Biol

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BackgroundPalmitic acid, the most common saturated free fatty acid, has been implicated in ER (endoplasmic reticulum) stress-mediated apoptosis. This lipoapotosis is dependent, in part, on the upregulation of the activating transcription factor-4 (ATF4). To better understand the mechanisms by which palmitate upregulates the expression level of ATF4, we integrated literature information on palmitate-induced ER stress signaling into a discrete dynamic model. The model provides an in silico framework that enables simulations and predictions. The model predictions were confirmed through further experiments in human hepatocellular carcinoma (HepG2) cells and the results were used to update the model and our current understanding of the signaling induced by palmitate.ResultsThe three key things from the in silico simulation and experimental results are: 1) palmitate induces different signaling pathways (PKR (double-stranded RNA-activated protein kinase), PERK (PKR-like ER kinase), PKA (cyclic AMP (cAMP)-dependent protein kinase A) in a time dependent-manner, 2) both ATF4 and CREB1 (cAMP-responsive element-binding protein 1) interact with the Atf4 promoter to contribute to a prolonged accumulation of ATF4, and 3) CREB1 is involved in ER-stress induced apoptosis upon palmitate treatment, by regulating ATF4 expression and possibly Ca2+ dependent-CaM (calmodulin) signaling pathway.ConclusionThe in silico model helped to delineate the essential signaling pathways in palmitate-mediated apoptosis.

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“…The discovery of the PKR-like ER kinase (PERK) (Harding et al, 1999) has cast doubts on the involvement of PKR in the inhibition of protein synthesis caused by depletion of ER calcium stores. However, it has recently been established that PKR is activated in addition to PERK upon induction of ER stress by both thapsigargin and tunicamycin (Onuki et al, 2004;Lee et al, 2007;Singh et al, 2009).…”

Section: Introductionmentioning

confidence: 99%