90-kDa ribosomal S6 kinase 1 is inhibited by S-glutathionylation of its active-site cysteine residue during oxidative stress

• RSK1 activity is inhibited by its S-glutathionylation at Cys223 residue.
• The EGF-induced activation of RSK1 was inhibited by oxidative stress.
• The oxidative stress prior to EGF stimulation results in inhibition of RSK1.
• EGF-induced nNOS phosphorylation at Ser847 is inhibited during oxidative stress.
• The novel cross talk between RSK1 and NO signaling is proposed.

Previously, we reported that p90-RSK1 phosphorylates neuronal nitric oxide synthase (nNOS) at Ser847 in cells treated with mitogens, leading to the inhibition of NOS activity. Here, we show RSK1 Cys223 glutathionylation limits the activity of the enzyme following an oxidative stimulus and attenuates the nNOS phosphorylation. Treatment of RSK1 with diamide/glutathione results in inactivation of the enzyme in vitro. Mutagenesis studies confirmed that S-glutathionylation of Cys223 is both necessary and sufficient for this inhibition of RSK1. In transfected cells expressing RSK1 and nNOS, treatment with diamide caused a decrease in EGF-induced phosphorylation of nNOS at Ser847. Cells expressing mutant RSK1 (C223S) proved resistant in this regard. Thus, RSK1 Cys223 glutathionylation may contribute to regulate the levels of NO in the brain.