Induction of nitric-oxide synthase and activation of NF-kappa B by interleukin-12 p40 in microglial cells

Interleukin-12 (IL-12) is composed of two different subunits, p40 and p35. Expression of p40 mRNA but not that of p35 mRNA in excessive amount in the central nervous system of patients with multiple sclerosis (MS) suggests th at IL-12 p40 may have a role in the pathogenesis of the disease. However, t he mode of action of p40 is completely unknown. Because nitric oxide produc ed from the induction of nitric-oxide synthase (iNOS) also plays a vital ro le in the pathophysiology of MS, the present study was undertaken to explor e the role of p40 in the induction of NO production and the expression of i NOS in microglia, Both IL-12 and p40(2), the p40 homodimer, dose-dependentl y induced the production of NO in BV-2 microglial cells. This induction of NO production was accompanied by an induction of iNOS protein and mRNA. Ind uction of NO production by the expression of mouse p40 cDNA but not that of the mouse p35 cDNA suggests that the p40 but not the p35 subunit of IL-12 is involved in the expression of iNOS, In addition to BV-2 glial cells, p40 , also Induced the production of NO in mouse primary microglia and peritone al macrophages. However, both IL-12 and p40, were unable to induce the prod uction of NO in mouse primary astrocytes. Because activation of NF-kappaB i s important for the expression of iNOS, we investigated the effect of p40, on the activation of NF-kappaB, Induction of the DNA binding as well as the transcriptional activity of NF-kappaB by p40, and inhibition of p40(2)-ind uced expression of iNOS by SN50, a cell-permeable peptide carrying the nucl ear localization sequence of p50 NF-kappaB, but not by SN50M, a nonfunction al peptide mutant, suggests that p40, induces the expression of iNOS throug h the activation of NF-kappaB. This study delineates a novel role of IL-12 p40 in inducing the expression of iNOS in microglial cells, which may parti cipate in the pathogenesis of neuroinflammatory diseases.