Exocytotic stimulation promotes association of the ADP-ribosylation factor with PC12 cell membranes

Heregulin promotes expression and subcellular redistribution of ADP-ribosylation factor 3

To identify genes whose expression is modulated by heregulin-beta1 (HRG), a regulatory polypeptide for mammary epithelial cells, we performed differential display screening of MCF-7 cell mRNA. One cDNA clone upregulated by HRG was identical to human ADP-ribosylation factor 3 (ARF3), a guanine nucleotide-binding protein functioning in vesicular trafficking, phospholipase D activation and intracellular transport. HRG treatment increased expression of ARF3 mRNA and protein. Also, HRG triggered a rapid redistribution of ARF3, first to cell membranes and then to the nuclear compartment, where ARF3 colocalized with acetylated histone H3 in discrete regions. In addition, the ARF3 protein was developmentally regulated in the mammary gland with the highest levels in virgin and post-weaning glands. Together, these findings suggest for the first time that stimulation of ARF3 expression, subcellular redistribution and interaction with acetylated histone H3 may play a role in the action of HRG in mammary epithelial cells.

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

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 (Gi/Go) 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 Gi/Go, causing inhibition of ADP-ribosylation by pertussis toxin.

Modifications of Ca2+ mobilization and noradrenaline release by S-nitroso-cysteine in PC12 cells

The effects of nitrogen monoxide (NO)-related compounds on cytosolic free Ca2+ concentrations ([Ca2+]i) and noradrenaline (NA) release in neurosecretory PC12 cells were investigated. The addition of S-nitroso-cysteine (SNC) stimulated [Ca2+]i increases from an intracellular Ca2+ pool continuously in a concentration-dependent manner. Other NO donors, which stimulate cyclic GMP accumulation, did not cause [Ca2+]i increases. After treatment with 0.2 mM SNC, transient increases in [Ca2+]i from the Ca2+ pool induced by caffeine were completely abolished. The addition of N-ethylmaleimide (NEM) caused sustained [Ca2+]i increases from the intracellular Ca2+ pool. Furthermore, caffeine did not stimulate further [Ca2+]i increases in PC12 cells pretreated with NEM. These findings suggest that SNC and NEM predominantly interact with a caffeine-sensitive Ca2+ pool. The addition of dithiothreitol (DTT) to 0.4 mM SNC-stimulated cells reduced [Ca2+]i to basal levels, and the addition of DTT to NEM-stimulated cells locked [Ca2+]i at high levels. The stimulatory effects of SNC but not NEM were not abolished by pretreatment with DTT. These findings suggest that modification of the oxidation status of the sulfhydryl groups on the caffeine-sensitive receptors by SNC or NEM regulates Ca2+ channel activity in a reversible manner. SNC did not stimulate NA release by itself but did inhibit ionomycin-stimulated NA release. In contrast, NEM stimulated NA release in the absence of extracellular CaCl2 and further enhanced ionomycin-stimulated NA release. Ca2+ mobilization by SNC from the caffeine-sensitive pool was not a sufficient factor, and other factors stimulating NA release may be negatively regulated by SNC.

Inhibition of noradrenaline release from PC12 cells by the long-term treatment with cholera toxin

Guanine nucleotide-binding (G) proteins are required for intracellular vesicular transport and endocytosis. In this study, we investigated the effects of short-term (2 h) and long-term (24 h) treatment with cholera toxin (CTX), which ADP-ribosylates proteins having arginine residues such as the alpha subunit of Gs (G(s alpha)), on exocytosis from the neurosecretory rat pheochromocytoma PC 12 cell line. Short-term treatment with CTX stimulated the accumulation of cyclic AMP, and synergistically enhanced both extracellular Ca2+-dependent [3H]noradrenaline (NA) releases (induced by high K+ and ATP) and Ca2+-independent release (induced by mastoparan, a peptide in wasp venom). Long-term treatment with CTX for 24h inhibited Ca2+-dependent and -independent stimulated [3H]NA release. The inhibitory effect of long-term CTX treatment was not derived from a cyclic AMP-dependent system, because (1) H-89, an inhibitor of protein kinase A, had no effect on the inhibition induced by CTX, (2) the long-term treatment with forskolin did not show an inhibitory effect. [32P]ADP-ribosylation of G(s alpha) and its immunoreactivity with anti-G(s alpha) antiserum in the crude membrane fraction was inhibited in the long-term CTX-treated cells, but not in the long-term forskolin-treated cells. [32P]ADP-ribosylation of G(s alpha) in the membrane fraction of short-term CTX-treated cells was approximately 90% of the level in the control cells. These findings suggest that CTX stimulates [3H]NA release via a cyclic AMP-dependent system in the short-term, and that long-term CTX treatment inhibited its release, maybe via ADP-ribosylation of CTX-sensitive proteins such as G(s alpha).