N-methyl-D-aspartate induces neurogranin/RC3 oxidation in rat brain slices

Neurogranin/RC3 (Ng), a postsynaptic neuronal protein kinase C (PRC) substr ate, binds calmodulin (CaM) at low level of Ca2+. In vitro, rat brain Ng ca n be oxidized by nitric oxide (NO) donors and by oxidants to form an intram olecular disulfide bond with resulting downward mobility shift on nonreduci ng SDS-polyacrylamide gel electrophoresis. The oxidized Ng, as compared wit h the reduced form, is a poorer substrate of PKC but like the PKC-phosphory lated Ng has a lower affinity for CaM than the reduced form. To investigate the physiological relevance of Ng oxidation, we tested the effects of neur otransmitter, N-methyl-D-aspartate (NMDA), NO donors, and other oxidants su ch as hydrogen peroxide and oxidized glutathione on the oxidation of this p rotein in rat brain slices. Western blot analysis showed that the NMDA-indu ced oxidation of Ng was rapid and transient, it reached maximum within 3-5 min and declined to base line in 30 min. The response was dose-dependent (E C50 similar to 100 mu M) and could be blocked by NMDA-receptor antagonist 2 -amino-5-phosphonovaleric acid and by NO synthase inhibitor N-G-nitro-L-arg inine methyl ester and N-G-monomethyl-L-arginine. Ng was oxidized by NO don ors, sodium nitroprusside, S-nitroso-N-acetylpenicillamine, and S-nitrosogl utathione, and H2O2 at concentrations less than 0.5 mM. Oxidation of Ng in brain slices induced by sodium nitroprusside could be reversed by dithiothr eitol, ascorbic acid, or reduced glutathione. Reversible oxidation and redu ction of Ng were also observed in rat brain extracts, in which oxidation wa s enhanced by Ca2+ and the oxidized Ng could be reduced by NADPH or reduced glutathione. These results suggest that redox of Ng is involved in the NMD A-mediated signaling pathway and that there are enzymes catalyzing the oxid ation and reduction of Ng in the brain. We speculate that the redox state o f Ng, similar to the state of phosphorylation of this protein, may regulate the level of CaM, which in turn modulates the activities of CaM-dependent enzymes in the neurons.