INHIBITION OF ENDOTHELIAL VASCULAR CELL-ADHESION MOLECULE-1 EXPRESSION BY NITRIC-OXIDE INVOLVES THE INDUCTION AND NUCLEAR TRANSLOCATION OF I-KAPPA-B-ALPHA

The induction of vascular cell adhesion molecule-1 (VCAM-1) expression by tumor necrosis factor (TNF)-alpha requires the activation of nucle ar factor-kappa B (NF-kappa B) via a process involving the phosphoryla tion and degradation of its cytoplasmic inhibitor, I kappa B alpha. We have shown that nitric oxide (NO) decreases VCAM-1 expression via inh ibition of NF-kappa B activation. To determine how NO inhibits NF-kapp a B, we studied the fate of I kappa B alpha following TNF-alpha stimul ation in the presence of NO donors S-nitrosoglutathione and sodium nit roprusside, Activation of NF-kappa B by TNF-alpha occurred within 15 m in and coincided with rapid degradation of I kappa B alpha, Go-treatme nt with NO donors did not prevent I kappa B alpha phosphorylation or d egradation, However, after 2 h of TNF-alpha stimulation, NO donors inh ibited NF-kappa B activation and augmented I kappa B alpha resynthesis and nuclear translocation by 2.5- and 3-fold, respectively, This corr elated with a 75% reduction in TNF-alpha-induced VCAM-1 expression. In a time-dependent manner, NO donors alone caused the nuclear transloca tion of I kappa B alpha. TO confirm that NO donors have similar effect s as endogenously derived NO, murine macrophage-like cells, RAW264.,7, were co-cultured with endothelial cells, Induction of RAW264.,7-deriv ed NO inhibited lipopolysaccharide-induced endothelial VCAM-1 expressi on, which was reversed by the NO synthase inhibitor N-omega-monomethyl -L-arginine. These findings indicate that NO inhibits NF-kappa B activ ation and VCAM-1 expression by increasing the expression and nuclear t ranslocation of I kappa B alpha.