Antioxidants reduce endoplasmic reticulum stress and improve protein secretion

Abstract

Protein misfolding in the endoplasmic reticulum (ER) contributes to the pathogenesis of many diseases. Although oxidative stress can disrupt protein folding, how protein misfolding and oxidative stress impact each other has not been explored. We have analyzed expression of coagulation factor VIII (FVIII), the protein deficient in hemophilia A, to elucidate the relationship between protein misfolding and oxidative stress. Newly synthesized FVIII misfolds in the ER lumen, activates the unfolded protein response (UPR), causes oxidative stress, and induces apoptosis in vitro and in vivo in mice. Strikingly, antioxidant treatment reduces UPR activation, oxidative stress, and apoptosis, and increases FVIII secretion in vitro and in vivo. The findings indicate that reactive oxygen species are a signal generated by misfolded protein in the ER that cause UPR activation and cell death. Genetic or chemical intervention to reduce reactive oxygen species improves protein folding and cell survival and may provide an avenue to treat and/or prevent diseases of protein misfolding.factor VIII ͉ oxidative stress ͉ unfolded protein response A lthough endoplasmic reticulum (ER) stress and oxidative stress are closely linked events, the molecular pathways that couple these processes are poorly understood (1). Reactive oxygen species (ROS) originate during oxygen-using cellular metabolic processes, such as oxidative phosphorylation within mitochondria. The ER provides a unique oxidizing environment for protein folding and disulfide bond formation before transit to the Golgi compartment. During disulfide bond formation ROS are formed as a product of electron transport from thiol groups in proteins through protein disulfide isomerase (PDI) and ER oxidoreductase 1 (ERO1) to reduce molecular oxygen to form the oxidant hydrogen peroxide. It has been suggested that oxidation of cysteine residues during disulfide bond formation in the ER may significantly contribute to oxidative stress (2, 3). The unfolded protein response (UPR) is an adaptive signaling pathway designed to prevent the accumulation of misfolded proteins in the ER lumen. Studies also suggest the UPR is designed to minimize the stress of oxidative protein folding (2). The UPR is signaled through the protein kinases inositolrequiring protein 1␣ and PKR-related ER kinase and the activating transcription factor 6␣ (4, 5). Chronic unresolved accumulation of unfolded proteins in the ER leads to apoptosis. To elucidate the relationship between unfolded protein accumulation in the ER lumen, oxidative stress, and apoptosis, we have analyzed the secretion of coagulation factor VIII (FVIII), a large glycoprotein that is deficient in the X chromosome-linked bleeding disorder hemophilia A. As FVIII is prone to misfolding in the ER lumen, FVIII expression provides a unique approach to manipulate the ER stress response that does not rely on pharmacological intervention, where any connection between ER stress and ROS would be difficult to dissect.FVIII is comprised of three domains in the ord...

Endoplasmic reticulum calcium release potentiates the ER stress and cell death caused by an oxidative stress in MCF-7 cells

“…Furthermore, the relationship between oxidative stress and ER stress is a matter of debate, because activation of the UPR can also result in ROS generation [50][51][52]. In our study, we found that pro-oxidant Asc/Men treatment induced the translational control arm of the UPR (by enhancing eIF2 phosphorylation) and upregulation of ER folding capacity (by the increase in GRP94 protein, one of the major ER chaperones).…”

“…These are still speculations and need further study. It has been proposed that BAPTA-AM interferes with Fenton's reaction [41,42] or may protect against a poorly defined pro-oxidative calciumassociated process, such as calcium-induced iron release [49] or ER stress-generated ROS production [50][51][52].…”

“…Furthermore, the relationship between oxidative stress and ER stress is a matter of debate, because activation of the UPR can also result in ROS generation [50][51][52]. In our study, we found that pro-oxidant Asc/Men treatment induced the translational control arm of the UPR A c c e p t e d M a n u s c r i p t 18 represent one of the pathways leading to this event; this observation also underlines the capacity of TG to trigger DNA fragmentation, as shown by others [43][44][45]57].…”

Role of endoplasmic reticulum stress in drug‐induced toxicity

“…It is also important to point out that ER stress and impaired protein folding can lead to the production of a significant amount of ROS (Malhotra and Kaufman 2007; Malhotra et al. 2008). Interestingly, it is estimated that 25% of the ROS generated in a cell results from the formation of disulfide bonds in the ER during normal protein synthesis (Tu and Weissman 2004; Sevier and Kaiser 2008).…”

Pathogenic obesity and nutraceuticals

“…One study investigated the expression of coagulation factor VIII, which is deficient in haemophilia A and is prone to misfolding in the ER (185) . It was found that factor VIII misfolding in the ER resulted in oxidative and ER stress in vitro in Chinese hamster ovary-(H9) cells with eventual apoptosis, which was attenuated by the addition of butylated hydroxyanisole, a phenolic, lipid-soluble antioxidant.…”