Role of Isoprenylcysteine Carboxyl Methyltransferase in Tumor Necrosis Factor- Stimulation of Expression of Vascular Cell Adhesion Molecule-1 in Endothelial Cells

We have previously shown that cytokine stimulation of the expression of vascular cell adhesion molecule-1 (VCAM-1), but not that of intercellular adhesion molecule-1 (ICAM-1), is redox sensitive in endothelial cells. Here, we investigated the role of isoprenylcysteine carboxyl methyltransferase (ICMTase), which methylates isoprenylated CAAX (where C indicates cysteine; A, aliphatic amino acids; and X, almost any other amino acid) proteins, including Rac1, a component of superoxide-generating NAD(P)H oxidase, in the expression of VCAM-1. Pretreatment of endothelial cells with N-acetyl-S-farnesyl-L-cysteine (AFC) or N-acetyl-S-geranylgeranyl-L-cysteine (AGGC), specific inhibitors of ICMTase, inhibited the tumor necrosis factor(TNF) stimulation of mRNA expression of VCAM-1 but not that of ICAM-1. Endothelial cells expressed constitutively active ICMTase, as suggested by the presence of methylated Rac1 and the methylation of AFC by the cells. TNFstimulation of the cells significantly increased the methylation of AFC and Rac1 in endothelial cells. That ICMTase was a component of the redox-sensitive signaling pathway was also suggested by the AFC inhibition of the generation of reactive oxygen species by TNF. Interestingly, the dominant-negative isoform of Rac1 was not selective but inhibited the TNFstimulation of the mRNA expression of VCAM-1 and ICAM-1. Thus, ICMTase is a critical component of the redox-sensitive VCAM-1–selective signaling pathway, and it appears to activate a discrete inflammatory signaling pathway, at least in part, through the methylation of Rac1. (Arterioscler Thromb Vasc Biol. 2002;22:759-764.)