Effects of S-Nitroso-Cysteine on Proteins That Regulate Exocytosis in PC12 Cells: Inhibitory Effects on Translocation of Synaptophysin and ADP-Ribosylation of GTP-Binding Proteins

Abstract

S-Nitroso-cysteine (SNC) inhibits Ca²⁺-induced noradrenaline (NA) release from PC12 cells. Since SNC stimulated Ca²⁺ mobilization from intracellular Ca²⁺ pools and SNC-induced inhibition of NA release was not washed-out, SNC may modify exocytosis-related proteins that overcome Ca²⁺ mobilization. In the present study, we investigated the effects of SNC on exocytosis-related proteins in PC12 cells. Ionomycin stimulated NA release and increased the immunoreactivity of synaptophysin in the cytosol fraction. A 25-kDa synaptosome-associated protein (SNAP-25), which localizes to plasma membranes and vesicles, increased in the cytosol fraction after stimulation. The increases in these proteins by ionomycin were inhibited in PC12 cells treated with 0.6 mM SNC. Synaptobrevin and synapsin-1 in the cytosol fraction, and syntaxin and 43 kDa growth-associated protein in the membrane fraction were not affected by ionomycin or SNC. Incubation of each protein with SNC did not affect antibody immunoreactivity. [³²P] ADP-ribosylation of GTP-binding proteins (G_i/G_o) by pertussis toxin, but not Gs by cholera toxin, was inhibited in SNC-treated PC12 cells and by co-addition of SNC to the assay mixture. These findings suggest that 1) SNC inhibits translocation of vesicles containing synaptophysin and SNAP-25, and 2) SNC reacts with cysteine residues in G_i/G_o, causing inhibition of ADP-ribosylation by pertussis toxin.