Expression of inducible
nitric oxide synthase (iNOS), which leads to the production of
nitric oxide (NO), is stimulated by
proinflammatory cytokines such as interleukin-1beta (
IL-1beta) and
tumor necrosis factor-alpha (
TNF-alpha). Here we report on the roles of nuclear factor-kappaB (
NF-kappaB) and
mitogen-activated protein (MAP)
kinases in
IL-1beta/TNF-alpha-induced iNOS expression in adult rat
astroglia. Cytokine-induced increases in
nitrite accumulation (an index of NO production) and iNOS expression were
attenuated by inhibition of
NF-kappaB with
pyrrolidine dithiocarbamate (PDTC). Similar
attenuation of these cytokine-induced responses was produced by inhibition of
MAP kinase (
MEK), the immediate upstream activator of Erk, using PD098,059. Combined treatment of
astroglia with PDTC and PD098,059 completely abolished the cytokine-induced increases in iNOS expression and
nitrite accumulation. By contrast, the
selective p38
kinase inhibitor SB203,580 amplified the effects of
IL-1beta/
TNF-alpha on
nitrite accumulation. In accordance with these findings, IL-1beta- and TNF-alpha-induced a time-dependent increase in Erk1/Erk2
activation. This
cytokine action was completely abolished by PD098,059 but was not altered by PDTC. Finally,
IL-1beta and
TNF-alpha induced degradation of NF-kappaB's bound
inhibitory protein, IkappaB-alpha, leading to
translocation of
NF-kappaB into the nucleus. IkappaB-alpha expression was not restored to control levels by inhibition of
MEK. Furthermore, inhibition of
MEK with PD098,059 did not alter IL-1beta- and TNF-alpha-induced expression of active
NF-kappaB. The results demonstrate that autonomous Erk and
NF-kappaB pathways mediate cytokine-induced increases in iNOS expression in
astroglia.
