CYCLIC-AMP POTENTIATION OF CYTOKINE-INDUCED NITRIC-OXIDE SYNTHASE ACTIVITY IN A MURINE ASTROCYTE CELL-LINE

Astrocytes in culture have been previously shown to express inducible nitric oxide synthase (iNOS) following treatment with cytokines such a s interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma). We report here on the effects of the cyclic nucleotide analogues 8-bromo- cyclic AMP and 8-bromo-cyclic GMP on cytokine-stimulated iNOS gene exp ression in a cultured murine astrocyte cell line. In these cells, neit her 8-bromo-cyclic AMP nor S-bromo-cyclic GMP alone was able to stimul ate iNOS activity. Similarly, neither IL-1 beta nor IFN-gamma was capa ble of independently stimulating iNOS expression. Co-stimulation with both cytokines, however, resulted in measurable increases in iNOS acti vity, and correlated to increases in iNOS mRNA levels. The addition of 8-bromo-cyclic AMP, but not 8-brorno-cyclic GMP, was found to further enhance the expression of iNOS activity induced by IL-1 beta and IFN- gamma co-stimulation. This potentiation effect of 8-bromo-cyclic AMP c orrelated to a further elevation in iNOS mRNA levels over that produce d by cytokine co-stimulation alone. However, 8-bromo-cyclic AMP co-tre atment with either cytokine alone did not stimulate iNOS activity, ind icating that the signal transduction pathway(s) involved in the potent iation effect of 8-bromo-cyclic AMP is functional only in the presence of both cytokines. These results indicate that cyclic AMP-mediated pr ocesses can participate in modulating the expression of astrocyte iNOS when the appropriate combinations of stimulatory cytokines are presen t. (C) 1997 Elsevier Science Ltd.