Title: Bidirectional regulation of neuronal nitric-oxide synthase phosphorylation at serine 847 by the N-methyl-D-aspartate receptor.
Authors: Rameau, Gerald A; Chiu, Ling-Yu; Ziff, Edward B
Published In J Biol Chem, (2004 Apr 02)
Abstract: At glutamatergic synapses, the scaffolding protein PSD95 links the neuronal isoform of nitric-oxide synthase (nNOS) to the N-methyl-d-aspartate (NMDA) receptor. Phosphorylation of nNOS at serine 847 (Ser(847)) by the calcium-calmodulin protein kinase II (CaMKII) inhibits nNOS activity, possibly by blocking the binding of Ca(2+)-CaM. Here we show that the NMDA mediates a novel bidirectional regulation of Ser(847) phosphorylation. nNOS phosphorylated at Ser(847) colocalizes with the NMDA receptor at spines of cultured hippocampal neurons. Treatment of neurons with 5 microm glutamate stimulated CaMKII phosphorylation of nNOS at Ser(847), whereas excitotoxic concentrations of glutamate, 100 and 500 microm, induced Ser(847)-PO(4) dephosphorylation by protein phosphatase 1. Strong NMDA receptor stimulation was likely to activate nNOS under these conditions because protein nitration to form nitrotyrosine, a marker of nNOS activity, correlated in individual neurons with Ser(847)-PO(4) dephosphorylation. Of particular note, stimulation with low glutamate that increased phosphorylation of nNOS at Ser(847) could be reversed by subsequent high glutamate treatment which induced dephosphorylation. The reversibility of NMDA receptor-induced phosphorylation at Ser(847) by different doses of glutamate suggests two mechanisms with opposite effects: 1). a time-dependent negative feedback induced by physiological concentrations of glutamate that limits nNOS activation and precludes the overproduction of NO; and 2). a pathological stimulation by high concentrations of glutamate that leads to unregulated nNOS activation and production of toxic levels of NO. These mechanisms may share pathways, respectively, with NMDA receptor-induced forms of synaptic plasticity and excitotoxicity.
PubMed ID: 14722119
MeSH Terms: Animals; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Calcium-Calmodulin-Dependent Protein Kinases/metabolism; Cells, Cultured; Cerebral Cortex/cytology; Glutamic Acid/metabolism; Hippocampus/cytology; Neuronal Plasticity/physiology; Neurons/cytology; Neurons/enzymology*; Nitric Oxide Synthase Type I; Nitric Oxide Synthase/metabolism*; Phosphoprotein Phosphatases/metabolism; Phosphorylation; Protein Phosphatase 1; Rats; Receptors, N-Methyl-D-Aspartate/metabolism*; Serine/metabolism; Synapses/enzymology