In brain astrocytes,
nuclear factor kappaB (
NF-kappaB) is activated by stimuli that produce cellular stress causing the expression of genes involved in defence, including the
inducible nitric oxide synthase (NOS-2). Theiler's murine encephalomyelitis virus (TMEV) induces a persistent
CNS infection and chronic immune-mediated
demyelination, similar to human
multiple sclerosis. The
cytokines interleukin (IL)-4 and
IL-10 inhibit the expression of proinflammatory
cytokines, counteracting the inflammatory process. Our study reports that
infection of cultured astrocytes with TMEV resulted in a time-dependent phosphorylation of
IkappaBalpha, degradation of
IkappaBalpha and
IkappaBbeta, activation of
NF-kappaB and expression of NOS-2. The
proteasome inhibitor MG-132 blocked TMEV-induced
nitrite accumulation, NOS-2
mRNA expression and phospho-
IkappaBalpha degradation, suggesting
NF-kappaB-dependent NOS-2 expression. Pretreatment of astrocytes with
IL-4 or
IL-10 decreased p65 nuclear translocation,
NF-kappaB binding activity and NOS-2 transcription.
IL-4 and
IL-10 caused an accumulation of
IkappaBalpha in TMEV-infected astrocytes without affecting
IkappaBbeta levels. The
IkappaB kinase activity and the degradation rate of both IkappaBs were not modified by either
cytokine, suggesting de novo synthesis of
IkappaBalpha. Indeed,
IL-4 or
IL-10 up-regulated
IkappaBalpha mRNA levels after TMEV
infection. Therefore, the accumulation of
IkappaBalpha might impair the translocation of the
NF-kappaB to the nucleus, mediating the inhibition of
NF-kappaB activity. Overall, these data suggest a novel mechanism of action of
IL-4 and
IL-10, which abrogates NOS-2 expression in viral-infected glial cells.