Proteasome inhibitors block VCAM-1 and ICAM-1 gene expression in endothelial cells without affecting nuclear translocation of nuclear factor-kappa B.

Endothelial cells play a major role in recruiting leukocytes to sites of inflammation. This is accomplished, at least in part, by up-regulation of cell surface adhesion molecules, including VCAM-1 and ICAM-1, in response to cytokines. In this report, we investigated the role of the proteasome complex in mediating the interleukin (IL)- 1 beta induction of VCAM-1 and ICAM-1 gene expression in human endothelial cells. We present evidence that a proteasome inhibitor, n-acetyl-leucinyl-leucinyl-norleucinal (norLEU), as well as specific protease inhibitors, n-tosyl-Lys-chloromethylketone and N-tosyl-Phe-chloromethylketone, blocked IL-1 beta induction of VCAM-1 and ICAM-1 promoter-driven reporter gene expression in stably transfected endothelial cells. These inhibitors also blocked cytokine induced cell surface expression of VCAM-1 and ICAM-1 by human umbilical vein endothelial cells. As expected, the protease inhibitors blocked the activation of nuclear factor (NF)-kappa B in response to IL-1 beta stimulation. In contrast, norLEU did not prevent IL-1 beta-induced nuclear translocation of NF-kappa B. The effects of norLEU were specific because it did not inhibit the IL-1 beta induction of plasminogen activator inhibitor type 1 gene expression. This study demonstrates that inhibition of the proteolytic activity of the proteasome blocks IL-1 beta induction of VCAM-1 and ICAM-1 gene expression in human endothelial cells.