Role of Isoprenylcysteine Carboxyl Methyltransferase in Tumor Necrosis Factor-α 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-alpha (TNF-alpha) 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. TNF-alpha stimulation 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-alpha. Interestingly, the dominant-negative isoform of Rac1 was not selective but inhibited the TNF-alpha stimulation 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.