Rac1 and Superoxide Are Required for the Expression of Cell Adhesion Molecules Induced by Tumor Necrosis Factor-α in Endothelial Cells

Oxidative signals play an important role in the regulation of endothelial cell adhesion molecule expression. Small GTP-binding protein Rac1 is activated by various proinflammatory substances and regulates superoxide generation in endothelial cells. In the present study, we demonstrate that adenoviral-mediated expression of dominant negative N17Rac1 (Ad.N17Rac1) suppresses tumor necrosis factor-α (TNF-α)-induced vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin gene expression in a dose-dependent manner. Ad.N17Rac1 did not inhibit TNF-α-induced activation of nuclear factor-κB (NF-κB) binding activity or inhibitor of NF-κB-α degradation. In contrast, Ad.N17Rac1 inhibited TNF-α-induced NF-κB-driven HIV(κB)4-CAT and p288VCAM-Luc promoter activity, suggesting that N17Rac1 inhibits TNF-α-induced VCAM-1, E-selectin, and ICAM-1 through suppressing NF-κB-mediated transactivation. In addition, expression of superoxide dismutase by adenovirus suppressed TNF-α-induced VCAM-1, E-selectin, and ICAM-1 mRNA accumulation. However, adenoviral-mediated expression of catalase only partially inhibited TNF-α-induced E-selectin gene expression and had no effect on VCAM-1 and ICAM-1 gene expression. These data suggest that Rac1 and superoxide play crucial roles in the regulation of expression of cell adhesion molecules in endothelial cells.