Inhibition of endothelial vascular cell adhesion molecule-1 expression by nitric oxide involves the induction and nuclear translocation of IκBα

The induction of vascular cell adhesion molecule-1 (VCAM-1) expression by tumor necrosis factor (TNF)-alpha requires the activation of nuclear factor-kappa B (NF-kappa B) via a process involving the phosphorylation and degradation of its cytoplasmic inhibitor, I kappa B alpha. We have shown that nitric oxide (NO) decreases VCAM-1 expression via inhibition of NF-kappa B activation. To determine how NO inhibits NF-kappa B, we studied the fate of I kappa B alpha following TNF-alpha stimulation in the presence of NO donors S-nitrosoglutathione and sodium nitroprusside, Activation of NF-kappa B by TNF-alpha occurred within 15 min and coincided with rapid degradation of I kappa B alpha, Go-treatment with NO donors did not prevent I kappa B alpha phosphorylation or degradation, However, after 2 h of TNF-alpha stimulation, NO donors inhibited NF-kappa B activation and augmented I kappa B alpha resynthesis and nuclear translocation by 2.5- and 3-fold, respectively, This correlated with a 75% reduction in TNF-alpha-induced VCAM-1 expression. In a time-dependent manner, NO donors alone caused the nuclear translocation of I kappa B alpha. TO confirm that NO donors have similar effects as endogenously derived NO, murine macrophage-like cells, RAW264.,7, were co-cultured with endothelial cells, Induction of RAW264.,7-derived NO inhibited lipopolysaccharide-induced endothelial VCAM-1 expression, which was reversed by the NO synthase inhibitor N-omega-monomethyl-L-arginine. These findings indicate that NO inhibits NF-kappa B activation and VCAM-1 expression by increasing the expression and nuclear translocation of I kappa B alpha.