Regulation of the unfolded protein response via S-nitrosylation of sensors of endoplasmic reticulum stress

Abstract

Protein S-nitrosylation modulates important cellular processes, including neurotransmission, vasodilation, proliferation, and apoptosis in various cell types. We have previously reported that protein disulfide isomerase (PDI) is S-nitrosylated in brains of patients with sporadic neurodegenerative diseases. This modification inhibits PDI enzymatic activity and consequently leads to the accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) lumen. Here, we describe S-nitrosylation of additional ER pathways that affect the unfolded protein response (UPR) in cell-based models of Parkinson’s disease (PD). We demonstrate that nitric oxide (NO) can S-nitrosylate the ER stress sensors IRE1α and PERK. While S-nitrosylation of IRE1α inhibited its ribonuclease activity, S-nitrosylation of PERK activated its kinase activity and downstream phosphorylation/inactivation or eIF2α. Site-directed mutagenesis of IRE1α(Cys931) prevented S-nitrosylation and inhibition of its ribonuclease activity, indicating that Cys931 is the predominant site of S-nitrosylation. Importantly, cells overexpressing mutant IRE1α(C931S) were resistant to NO-induced damage. Our findings show that nitrosative stress leads to dysfunctional ER stress signaling, thus contributing to neuronal cell death.

Targeting protein disulfide isomerase with the flavonoid isoquercetin to improve hypercoagulability in advanced cancer

“…For instance, PDI regulates HIV-1 entry into lymphocytes through disulfide exchange of HIV-associated glycoprotein 120 (5,51,52). Pathologic alterations in PDI activity in the endoplasmic reticulum are central to the unfolded protein response observed in aggressive malignancies and neurodegenerative diseases (1,2,(53)(54)(55)(56)(57). Targeting PDI has shown promise in animal models of Parkinson's disease and amylotrophic lateral sclerosis (50,58), and small-molecule inhibitors are under investigation as a chemotherapeutics for a range of cancers, including ovarian cancer (59), multiple myeloma (60), and hepatocellular carcinoma (61).…”

Modulation of Unfolded Protein Response by Methylmercury

“…We previously found that NO elicited ER stress and then promoted IRE1α phosphorylation. 9) Interestingly, the ribonuclease activity of IRE1α was strongly abolished via the S-nitrosylation of the kinase-extension nuclease (KEN) domain in IRE1α, although phosphorylated IRE1α was detected.…”

“…We earlier demonstrated that inositol-requiring enzyme 1α (IRE1α), a sensor of ER stress that is located within the ER membrane, is also directly modified and regulated by NO. 9) This modification leads to the inhibition of endonuclease activity, thereby attenuating the splicing of immature XBP1 mRNA. Because nucleophiles such as NO and MeHg easily react with protein thiols and affect enzymatic activity or function, it is important to determine its molecular targets and to characterize their effects on cells.…”

Nitric oxide-mediated pathways and its role in the degenerative diseases

“…S-nitrosylation also abrogates PDImediated attenuation of neuronal cell death triggered by ERS (11). In addition to PDI, S-nitrosylation is also likely to affect critical thiol groups on other ERS sensors, such as IRE1 and PERK (12). While S-nitrosylation of IRE1 inhibited its ribonuclease activity, S-nitrosylation of PERK activated its kinase activity and downstream phosphorylation/inactivation of eIF2.…”

“…Researches also showed the involvement of NO in other biological processes of PD, such as ERS and autophagy. NO can S-nitrosylate sensors of ERS via the unfolded protein response, which contributes to the etiology of PD (48). During the pathogenesis of PD, the accumulation of immature and denatured proteins results in ER dysfunction, but the upregulation of PDI represents an adaptive response to protect neurons.…”