Proteasome inhibitors block VCAM‐1 and ICAM‐1 gene expression in endothelial cells without affecting nuclear translocation of nuclear factor‐ϰB

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)‐1β 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‐1β 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)‐ϰB in response to IL‐1β stimulation. In contrast, norLEU did not prevent IL‐1β‐induced nuclear translocation of NF‐ϰB. The effects of norLEU were specific because it did not inhibit the IL‐1β induction of plasminogen activator inhibitor type 1 gene expression. This study demonstrates that inhibition of the proteolytic activity of the proteasome blocks IL‐1β induction of VCAM‐1 and ICAM‐1 gene expression in human endothelial cells.