Cell type-specific transactivation of the VCAM-1 promoter through an NF-κB enhancer motif

Abstract

Cytokine activation of vascular cell adhesion molecule-1 (VCAM-1) gene expression by endothelial cells is an important feature in a variety of vascular inflammatory responses. Cytokines transcriptionally activate the VCAM-1 promoter in endothelial cells at least in part through two closely linked NF-κB enhancer motifs, κL-κR (positions -77 and -63). However, cytokine activation of the dimeric NF-κB transcriptional factor (p50+p65 subunits) occurs in almost all cell types, whereas VCAM-1 gene expression exhibits a cell type-specific pattern of expression. Tumor necrosis factor-α markedly transactivated a transiently transfected minimal κL-κR motif-driven VCAM-1 promoter, p85VCAMCAT, in passaged human vascular endothelial cells but not in the human epithelial cell line, HeLa suggesting that cell type-specific factors may function through the κL-κR motif. Both cell types exhibited similar inductions of NF-κB DNA binding activity and transcriptional activity. However, co-transfection of HeLa cells with p65 and p50 expression vectors demonstrated that the minimal VCAM-1 promoter was effectively transactivated by p65 alone but that additional co-expression of p50 blocked this activity. Furthermore, cytokine activation of the minimal VCAM-1 promoter in HeLa cells was recovered by inhibition of p50 expression using antisense oligonucleotide. These studies suggest that the NF-κB(p50+p65 heterodimer) does not support transactivation of the VCAM-1 promoter with the p50 subunit potentially playing a significant inhibitory role in suppressing cytokine activation of VCAM-1. In addition, p65 associated transcriptional factors other than NF-κB may serve as positive, cytokine-inducible, cell type-specific regulators of VCAM-1 gene expression.