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Endoplasmic reticulum stress exacerbates ischemia-reperfusion-induced apoptosis through attenuation of Akt protein synthesis in human choriocarcinoma cells

Hong-wa Yung^*, Svitlana Korolchuk^*, Aviva M. Tolkovsky, D. Stephen Charnock-Jones and Graham J. Burton^*,1

^* Department of Physiology, Development and Neuroscience,

Department of Biochemistry and

Department of Obstetrics and Gynaecology, University of Cambridge, Cambridge, UK

¹Correspondence: Department of Physiology, Development and Neuroscience, Physiological Laboratory, Downing St., Cambridge CB2 3EG, UK. E-mail: gjb2{at}cam.ac.uk

Oxidative stress is central to ischemia-reperfusion injury. The role of the endoplasmic reticulum (ER) in this process is uncertain. In ER signaling, PERK-Nrf2 and Ire-CHOP are two pathways that determine cell fate under stress. PERK-Nrf2 up-regulates antioxidant enzyme expression whereas Ire-CHOP promotes apoptosis. We have identified a novel pathway in ER stress-induced apoptosis after ischemia-reperfusion in vitro involving translational suppression of the survival kinase PKB/Akt (Akt), and elucidated an alternative protective role of antioxidants in the regulation of Akt activity. Using human choriocarcinoma JEG-3 cells, we found that sustained activation of ER stress by tunicamycin or thapsigargin exacerbated apoptosis in oxygen-glucose-deprived cells during reoxygenation. This was mediated via a reduction in phosphorylated Akt secondary to down-regulation of protein translation rather than suppression of phosphorylation. Transient overexpression of wild-type Akt, but not kinase-dead Akt, in JEG-3 cells diminished tunicamycin-OGD reoxygenation-induced apoptosis. The antioxidants Trolox and Edaravone reduced apoptosis, but the protective effect of Trolox was abrogated by the PI3K inhibitor, LY294002. We speculate that sustained ER stress may contribute to the placental dysfunction seen in human pregnancy complications.—Yung, H-w., Korolchuk, S., Tolkovsky, A. M., Charnock-Jones, D. S., Burton, G. J. Endoplasmic reticulum stress exacerbates ischemia-reperfusion-induced apoptosis through attenuation of Akt protein synthesis in human choriocarcinoma cells.

Key Words: unfolded protein response • placenta • oxidative stress • trophoblast • CHOP

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