Comparison of the signal transduction pathways for the induction of gene expression of nitric oxide synthase-2 in response to two different stimuli.

Human optic nerve astrocytes induce nitric oxide synthase-2 (NOS-2) in vitro in response to cytokines (interferon-gamma/interleukin-1beta) and elevated hydrostatic pressure. Using relatively specific inhibitors, we have compared induction of NOS-2 in response to these two stimuli to determine whether the same or different signal transduction pathways participate in the responses. Using SN50 and CAGE, which inhibit the NFkappaB pathway, the induction of NOS-2 in response to both cytokines and elevated hydrostatic pressure was blocked. Using SB202190 and SB203580, which inhibit p38 mitogen-activated protein kinase, only the response to cytokines was blocked. In contrast, when inhibitors of epidermal growth factor receptor tyrosine kinase AG 82 and AG 18 were used, the induction of NOS-2 in response to pressure, but not in response to cytokines, was blocked. Signal transduction pathways presumably regulate the synthesis of NOS-2 through downstream events that induce transcription of the NOS-2 gene. Our data suggest that activation of different sites in the promoter region of the NOS-2 gene is needed for these different stimuli to induce NOS-2.