Role of activating protein-1 in the regulation of the vascular cell adhesion molecule-1 gene expression by tumor necrosis factor-α

Abstract

Endothelial cell surface expression of VCAM-1 is one of the initial steps in the pathogenesis of atherosclerosis. The inflammatory response transcription factor nuclear factor (NF)-κB plays an important role in the regulation of VCAM-1 expression by various stimuli including tumor necrosis factor (TNF)-α. Other transcription factors may modulate this response through interaction with NF-κB factors. Since c-Fos/c-Jun (activating protein-1 (AP-1)) are expressed in vascular endothelium during proinflammatory conditions, we investigated the role of AP-1 proteins in the expression of VCAM-1 by TNF-α in SV40 immortalized human microvascular endothelial cells (HMEC). TNF-α induced expression of both early protooncogenes, c-fos and c-jun. The ability of TNF-α to activate the κB- motif (κL-κR)-dependent VCAM-1 promoter-chloramphenicol acetyltransferase (CAT) reporter gene lacking a consensus AP-1 element was markedly inhibited by co-transfection of the expression vector encoding c-fos ribozyme, which decreases the level of c-fos by degrading c-fos mRNA, or c-fos or c-jun oligonucleotides. Conversely, co-transfection of c-Fos and c-Jun encoding expression vectors potentiated the p65/NF-κB-mediated transactivation of the VCAM-1 promoter-CAT reporter gene. Furthermore the c-Fos encoding expression vector potentiated by 2-fold the transactivation activity of a chimeric transcriptional factor Gal/p65 (containing the transactivation domain of p65 and the DNA binding domain of the yeast transcriptional factor Gal-4). Consistent with the promoter studies, curcumin and NDGA, inhibitors of AP-1 activation, markedly inhibited the ability of TNF-α to activate the expression of VCAM-1 mRNA levels at concentrations that did not inhibit the activation of NF-κB. In gel mobility supershift assays, the antibodies to c- Fos or c-Jun inhibited the binding of TNF-α-activated nuclear NF-κB to the κL-κR, suggesting that both c-Fos and c-Jun interacted with NF-κB. These results suggest that AP-1 proteins may mediate the effect of TNF-α in the regulation of VCAM-1 expression through interaction with NF-κB factors in endothelial cells.