Forskolin inhibits expression of inducible nitric oxide synthase mRNA via inhibiting the mitogen activated protein kinase in C6 cells

This study has demonstrated the mechanism of protein kinase A (PKA)-dependent inhibition of astrocytic nitric oxide production and inducible NO synthase mRNA expression induced by lipopolysaccharide. In C6 glioma cells, the stimulation with lipopolysaccharide (LPS; 1 mug/ml) evoked increases of nitric oxide (NO) production, NO synthase (iNOS) mRNA expression, phosphorylation of p38 mitogen activated protein kinase (p-p38), and the activation of NF kappaB. LPS-induced NO production and iNOS mRNA expression were inhibited by the pretreatment with forskolin (FSK; 5 muM) in a dose-dependent manner, and which were reversed by PKA inhibition by compound H89. Furthermore, LPS-induced increases of p-p38, but not activation of NF kappaB, were also reduced by FSK and H89 reversed the FSK-induced inhibition response. The dose-dependent inhibition of NO production and iNOS mRNA expression by compound SB203580 (p38 inhibitor) suggests the participation of p38 in PKA-dependent inhibition of LPS-induced NO production and iNOS mRNA expression. However. the activation of NF kappaB by LPS also not affected by SB203580. Therefore, our results suggest that, in C6 glioma cells, LPS-induced NO production acid iNOS gene expression may be regulated by PKA pathway through the reduction of activity of p38 kinase. This inhibitory role of PRA may not involve the activation of NF kappaB. (C) 2001 Elsevier Science B.V. All rights reserved.