Regulation of trascription factor by GABA_B mechanisms in cultured neuronal cells

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It this study, the effect of gamma-hydroxybutyric acid (GHB) in nuclear cyclic AMP responsive element (CRE) -and activator protein 1 (AP-1) DNA-binding activities in primary neuronal cultured cellswas examined. Gel-shift assays showed that exposure of the cells to GHB (1mM) increased nuclear CRE-and AP-1 DNA-binding activities in cultured mouse cerebellar granule cells and cerebral cortical cells. These increases in nuclear DNA-binding activities in cultured mouse cerebellar granule cells were antagonized by specific GABA_B antagonists such as CGP 55845 (1muM) and CGP 35348 (1mM). In addition, treatment of the cells with 1,2-bis (2'-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid tetraacetoxymethyl ester (BAPTA-AM), an intracellular Ca^<2+> chelating agent, or thapsigargin, an endoplasmic reticulum Ca^<2+>-ATPase inhibitor, suppressed the GHB-induced increases in nuclear DNA-binding activities. Furthermore, the GHB-induced increases in nuclear CRE-and AP-1 DNA-binding activities were suppressed by treatment with calmodulin kinase II inhibitors such as KN-62 (10muM) and KN-93 (10muM). In addition, the CRE-binding activity was completely supershifted by the CRE-binding protein (CREB) antibody, and was eliminated by the phospholyrated CREB antibody. The AP-1 DNA-binding activity was blocked by c-Jun and c-Fos antibodies. These results siggest that stimulation of GABA_B receptors by GHB activates intracellular Ca2+ storage sites and that increased intracellular Ca^<2+> plays an important role in elevation of nuclear CRE-and AP-1 DNA-binding activities and that calmodulin kinase II plays an important role in DHB-induced increases in both DNA-binding activities in cultured cerebellar granule cells. It is also suggested that GHB promotes the phosphorylation of CREB.