SUPPRESSION OF ASTROGLIAL NITRIC-OXIDE SYNTHASE EXPRESSION BY NOREPINEPHRINE RESULTS FROM DECREASED NOS-2 PROMOTER ACTIVITY

We previously demonstrated that norepinephrine (NE) inhibits induction of the calcium-independent isoform of nitric oxide synthase (NOS-2) i n primary rat astrocyte cultures. However, the molecular mechanisms un derlying this effect are unknown. In C6 cells and astrocytes, NE suppr essed both cytokine- and lipopolysaccharide (LPS)-dependent nitrite ac cumulation, an index of NOS-2 activity, NE reduced the steady-state le vels of NOS-2 mRNA induced by LPS plus cytokines but did not decrease NOS-2 mRNA stability or inhibit activation or subunit composition of t ranscription factor nuclear factor KB, which is necessary for NOS-2 in duction. In C6 cells stably transfected with a 1,588-bp mouse NOS-2 pr omoter, NE reduced LPS plus cytokine-induced reporter gene expression, suggesting inhibition of NOS-2 promoter activity. in contrast, suppre ssion was lost when a truncated 85-bp NOS-2 promoter was used, and in these cells NE potentiated reporter gene expression, alone or in the p resence of LPS and cytokines. These results suggest that the suppressi ve effects of NE are due to modification of transcription factor activ ity in a region located between -1,588 and -85 of the NOS-2 promoter a nd may help explain observations that in some cells cyclic AMP can pot entiate, rather than suppress, NOS-2 expression.