Postinduction transcriptional repression of E-selectin and vascular cell adhesion molecule-1.

Abstract

TNF-alpha induction of the E-selectin and vascular cell adhesion molecule-1 (VCAM-1) genes leads to transient accumulation of high levels of mRNA in endothelial cells. The increase in these mRNAs after induction is due to an increase in the rate of gene transcription, which is maintained for several hours in the continuous presence of cytokine. Cytokine-induced transcriptional activation of these genes requires the transcription factor, nuclear factor-kappaB. Following removal of TNF-alpha, there is rapid postinduction transcriptional repression common to both of these genes. The repression is protein synthesis dependent and correlates with protein synthesis-dependent loss of both the p50 and p65 subunits of nuclear factor-kappaB from the nucleus. IkappaBalpha is capable of specifically displacing endothelial-derived heterodimeric p50/p65 from the E-selectin and VCAM-1 kappaB elements, while having no effect on binding of p50 homodimer. In the presence of agents that block proteasomal degradation of IkappaBalpha, endogenous IkappaBalpha can be visualized in the nucleus of both resting and TNF-alpha-activated endothelial cells. Endogenous IkappaBalpha is readily detected in the nucleus of HeLa cells, and its nuclear localization is increased following removal of TNF-alpha. Repression of E-selectin and VCAM-1 transcription following cytokine removal requires the loss of nuclear p50 and p65, and involves IkappaBalpha. This postinduction transcription repression mechanism may be one component of a program that prevents inappropriate and prolonged expression of adhesion molecules.