Involvement of P38MAP kinase in the induction of nitric oxide synthase in human astrocytes

The present study underlines the importance of p38 mitogen-activated protein kinase (p38MAPK) in regulating the expression of iNOS in human astroglia. The combination of IL-1β and IFN-γ activated p38MAPK and induced the production of NO and the expression of iNOS in human U373MG astroglial cells. SB203580, a specific inhibitor of p38MAPK, and Dp38, a dominant-negative mutant of p38MAPK, markedly inhibited cytokine-induced production of NO and expression of iNOS. Next we investigated the role of NF-κB in the expression of iNOS. Inhibition of cytokine-induced NF-κB activation and iNOS expression by SN50, a specific inhibitor of p50 NF-κB, but not by SN50M, a nonfunctional peptide mutant, does suggest that activation of NF-κB is necessary for the expression of iNOS. However, SB203580 and Dp38 had no effect on the activation of NF-κB suggesting that SB203580 and Dp38 inhibit the expression of iNOS without inhibiting the activation of NF-κB. Next we examined the role of C/EBP-b in the expression of iNOS. In contrast to the effect of SB203580 and Dp38 on the activation of NF-κB, both SB203580 and Dp38 markedly inhibited the activation of C/EBP-b in cytokine-stimulated cells. Similar to U373MG astrocytoma cells, Dp38 also inhibited cytokine-induced expression of iNOS and activation of C/EBP-b but not that of NF-κB in human primary astroglia. Taken together, these studies suggest that p38MAPK regulates the expression of iNOS in human astroglia by regulating the activation of C/EBP-b but not that of NF-κB. Acknowledgements:  This study was supported by NIH grants (NS39940 and AG19487).