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Vol. 54, Issue 2, 258-263, August 1998
Department of Pharmacology, Johannes Gutenberg University, 55101 Mainz, Germany
Neuronal-type nitric oxide synthase (NOS I) is involved in
ischemia-induced brain damage, and glucocorticoids have been reported to protect from brain damage. This prompted us to investigate if the
activity or expression of NOS I was influenced by glucocorticoids. We
used the murine neuroblastoma cell line N1E-115 as our experimental model. Short-term incubation (30 min) of the N1E-115 cells with dexamethasone (10 nM to 1 µM) or
hydrocortisone (100 nM to 10 µM) did not
change the enzymatic activity of NOS I. However, the glucocorticoids
inhibited NOS I mRNA expression in a concentration-dependent fashion
(down to 53.3 ± 2.5% of control). In time-course experiments with 100 nM dexamethasone, maximum down-regulation of NOS I
mRNA was seen after 24 hr (55.6 ± 6.3% of control). Similar
effects were seen with 10 µM hydrocortisone. The effect
of 100 nM dexamethasone was completely reversed by 1 µM of the glucocorticoid receptor antagonist
mifepristone. In experiments with actinomycin D (10 µg/ml), the
half-life of the NOS I mRNA was determined to be approximately 12 hr
and remained unchanged after glucocorticoid incubation. Nuclear run-on
analyses indicated that the decrease in NOS I mRNA was the result of a
glucocorticoid-induced inhibition of NOS I gene transcription. In
Western blots, the 160-kDa NOS I protein band was down-regulated to
68.5 ± 8.4% of control after an incubation of the N1E-115 cells
with 100 nM dexamethasone for 26 hr. Similarly, NO
production was down-regulated to 57.8 ± 8.7% of control. These data demonstrate that glucocorticoids reduce the expression of NOS I
without changing its activity.
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