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

Abstract

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 downregulation 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. Keywordsunfolded protein response; placenta; oxidative stress; trophoblast; CHOP PLACENTAL OXIDATIVE STRESS has been postulated to be a key factor in the pathogenesis of human pregnancy complications such as intrauterine growth retardation and pre-eclampsia (1,2). We recently proposed that the cause of the stress is an ischemia-reperfusion type injury (3). Unlike in other organs, where ischemia-reperfusion injury is usually an isolated insult caused by pathological blockage or rupture of blood vessels attenuating oxygen and nutrient supply, in the placenta mild ischemia-reperfusion is likely to be a repetitive process. Maternal blood flow through the intervillous space of the placenta may fluctuate through three principal mechanisms: intrinsic contraction of the spiral arteries supplying the placenta, external 1Correspondence:

Evidence of Placental Translation Inhibition and Endoplasmic Reticulum Stress in the Etiology of Human Intrauterine Growth Restriction

“…22 Recently, we showed that I/R induces ER stress in the human trophoblast-like cell line, JEG-3 choriocarcinoma cells, and that this is associated with inhibition of protein synthesis. 23 One of the consequences we observed was reduced concentrations of both phosphorylated and total AKT. AKT signaling plays a central role in the regulation of cell growth and proliferation by integrating the actions of growth factors and functioning as an ATP and amino acid sensor to fine tune protein synthesis to nutrient availability via control of the mammalian target of rapamycin (mTOR) pathway and glycogen synthase kinase 3 (GSK-3) activity, respectively.…”

“…23 Human choriocarcinoma JAR cells were a gift from Dr. Ashley Moffett and were grown in RPMI 1640 medium (Invitrogen Ltd, Paisley, UK) supplemented with 5% heat-inactivated fetal bovine serum (Invitrogen), penicillin (100 U/ml), and streptomycin (100 g/ml) at 37°C in a 5% CO 2 atmosphere.…”

The Endoplasmic Reticulum Stress of Placental Impoverishment

“…In this issue of the AJP, Yung and colleagues 1 demonstrate that protein synthesis inhibition and ER stress play key roles in the pathophysiology of intrauterine growth restriction. One should also consider the authors' earlier study examining ER stress in the choriocarcinoma cell line JEG-3, 14 which could be induced by deprivation of oxygen and glucose or by tunicamycin. The authors singled out the survival kinase AKT (also known as protein kinase B) for detailed study.…”

Inositol-requiring enzyme 1-mediated endoplasmic reticulum stress triggers apoptosis and fibrosis formation in liver cirrhosis rat models

“…Previous studies have commonly reported that endoplasmic reticulum (ER) stress plays a crucial role in the induction and regulation of apoptosis (7,8). There are numerous pathways involved in ER stress, such as ER-associated protein degradation and the unfolded protein response (UPR) (9) The UPR pathway also activates several proteins, including inositol-requiring enzyme (IRE) 1, protein kinase R-like ER kinase (Perk) and activating transcription factor 6 (ATF6) (10).…”