%0 Journal Article
%T Redox Regulation of Protein Function via Cysteine S-Nitrosylation and Its Relevance to Neurodegenerative Diseases
%A Mohd Waseem Akhtar
%A Carmen R. Sunico
%A Tomohiro Nakamura
%A Stuart A. Lipton
%J International Journal of Cell Biology
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/463756
%X Debilitating neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), can be attributed to neuronal cell damage in specific brain regions. An important hallmark of these diseases is increased oxidative and nitrosative stress that occurs via overproduction of highly reactive free radicals known as reactive oxygen species (ROS) and reactive nitrogen species (RNS). These molecules are normally removed by cellular antioxidant systems. Under physiological conditions, ROS/RNS are present at low levels, mediating several neurotrophic and neuroprotective signaling pathways. In contrast, under pathological conditions, there is a pronounced increase in ROS/RNS generation, impairing normal neurological function. Nitric oxide (NO) is one such molecule that functions as a signaling agent under physiological conditions but causes nitrosative stress under pathological conditions due to its enhanced production. As first reported by our group and colleagues, the toxic effects of NO can be in part attributed to thiol S-nitrosylation, a posttranslational modification of cysteine residues on specific proteins. Here, we review several reports appearing over the past decade showing that S-nitrosylation of an increasing number of proteins compromises important cellular functions, including mitochondrial dynamics, endoplasmic reticulum (ER) protein folding, and signal transduction, thereby promoting synaptic damage, cell death, and neurodegeneration. 1. Introduction A delicate balance in redox state exists in cells, in large part because of production of ROS/RNS and the antioxidant systems that detoxify them. This homeostatic redox balance maintains a relatively low concentration of ROS/RNS. Under physiological conditions, ROS/RNS can activate specific signaling pathways required for diverse cellular functions, including cell growth and immune responses [1]. However, increased ROS/RNS production or decreased antioxidant capacity can lead to perturbation of the redox balance, causing oxidative/nitrosative stress [2] (Figure 1). We and others have demonstrated that sustained oxidative/nitrosative stress elicits counterattack mechanisms, including activation of transcriptional pathways that activate (i) endogenous antioxidant phase 2 enzymes (the Keap1/Nrf2 cascade) and (ii) chaperones for refolding misfolded proteins (heat-shock proteins of the Hsp90/HSF1 cascade). These transcription pathways can be activated directly by ROS/RNS or by electrophilic compounds generated in response to oxidation [3¨C6]. For example, upon reaction of an electrophile
%U http://www.hindawi.com/journals/ijcb/2012/463756/