TNF-α and 9-cis-Retinoic Acid Synergistically Induce ICAM-1 Expression: Evidence for Interaction of Retinoid Receptors with NF-κB

Abstract

TNF-α and 9-cis-retinoic acid (9-cis-R) synergistically enhance ICAM-1 protein expression in immortalized human aortic endothelial cells (HAECTs). At a TNF-α concentration of 0.1 ng/ml, 1 μM 9-cis-R enhanced ICAM-1 protein expression 4-fold. Treatment with 1 μM 9-cis-R alone caused no induction of ICAM-1 expression. Functional analysis of human ICAM-1 promoter–luciferase constructs revealed that the synergism was attributable to transcriptional regulation. Expression of a luciferase reporter vector containing a 311-bp fragment of the ICAM-1 promoter (−252 to +59 bp relative to the transcriptional start site) was increased 2.9- and 4.9-fold by treatment with 9-cis-R and TNF-α, respectively, while cotreatment with 9-cis-R and TNF-α induced expression to 19.9-fold. Mutation studies revealed that RARE and NF-κB sites located respectively at −226 and −188 bp relative to the transcription start site are essential for the synergistic control of promoter activity. Mutation of either the RARE or the NF-κB site eliminated the synergistic enhancement of promoter activity. Moreover, mutation of the RARE abrogated promoter activity induced by treatment with TNF-α alone and mutation of the NF-κB site eliminated promoter activity induced by treatment with 9-cis-R alone. We conclude that retinoid receptors and NF-κB act in concert at the promoter level to facilitate ICAM-1 expression in endothelial cells.