Nature Publishing Group Acta Medica Okayama 2045-2322 5 2015 Regulation of the unfolded protein response via S-nitrosylation of sensors of endoplasmic reticulum stress 14812 EN Nakato Ryosuke Ohkubo Yu Konishi Akari Shibata Mari Kaneko Yuki Iwawaki Takao Nakamura Tomohiro Lipton Stuart A. Uehara Takashi 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 IRE1ƒ¿ and PERK. While S-nitrosylation of IRE1ƒ¿ inhibited its ribonuclease activity, S-nitrosylation of PERK activated its kinase activity and downstream phosphorylation/inactivation or eIF2ƒ¿. Site-directed mutagenesis of IRE1ƒ¿(Cys931) prevented S-nitrosylation and inhibition of its ribonuclease activity, indicating that Cys931 is the predominant site of S-nitrosylation. Importantly, cells overexpressing mutant IRE1ƒ¿(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. No potential conflict of interest relevant to this article was reported.