A functional role of I kappa B-epsilon in endothelial cell activation

The NF-kappa B inhibitor I kappa B-epsilon is a new member of the I kappa B protein family, but its functional role in regulating NF-kappa B-mediated : induction of adhesion molecule expression is unknown, In vascular endothe lial cells, I kappa B-epsilon associates predominantly with the NF-kappa B subunit Rel A and to a lesser extent with c-Rel, whereas I kappa B-alpha an d I kappa B-beta associate with Rel A only. Following stimulation with TNF- alpha, pyrrolidine dithiocarbamate (PDTC), N-acetylcysteine, and dexamethas one prevented I kappa B kinase-induced I kappa B-alpha, but not I kappa B-b eta or I kappa B-epsilon phosphorylation and degradation. Since the activat ion of NF-kappa B is required for the induction of adhesion molecule expres sion, we examined the role of I kappa B-epsilon in the transactivation of p romoters from VCAM-1, ICAM-1, and E-selectin, Using reporter gene construct s of adhesion molecule promoters, PDTC inhibited VCAM-1 and E-selectin, but to a lesser extent, ICAM-1 promoter activity. Subcloning of kappa B cis-ac ting elements of VCAM-1, E-selectin, and ICAM-1 into a heterologous promote r construct revealed that PDTC inhibited VCAM-1 and E-selectin, but to a le sser extent, ICAM-1 kappa B promoter activity, By electrophoretic mobility shift assay, NF-kappa B heterodimers containing c-Rel specifically bind to the kappa B motif in the ICAM-1, but not VCAM-1 or E-selectin promoter. Ind eed, overexpression of c-Rel induced ICAM-1 KB promoter activity to a great er extent than that of E-selectin and overexpression of I kappa B-epsilon i nhibited ICAM-1 and VCAM-1 promoter activity in endothelial cells. These fi ndings indicate that c-Rel-associated I kappa B-epsilon is involved in the induction of ICAM-1 expression.