W - KB Subunit - specific Regulation of the IKBCU Promoter *

Stimulation of endothelial cells by cytokines and bacterial lipopolysaccharide leads to activation f the transcription factor NF-KB. NF-KB in turn regulates the expression of several genes involved in the inflammatory reaction, including cell adhesion molecules, interleukins, and transcription factors. One of these induced genes encodes an inhibitor of NF-KB, ECI-~/IKB~, that contains in its 5‘ regulatory region six consensus binding sites for NF-KB. We demonstrate here that these sites display striking differences in their ability in vitro to bind to various NF-KB subunits. In vivo, all six sites contribute, though to varying degrees, to transcription from the ECI-G/IKBa promoter, as demonstrated by deletion and mutation analysis. Among the NF-KB subunits tested p65, the p65/p50 heterodimer and, to a lesser extent, c-Rel, are able to activate transcription, whereas p50 or p50/RelB were inactive. Since many genes regulated by NF-KB contain only one or two DNA-binding sites for this transcription factor, the presence of six functional NF-KB-binding sites in the ECI-6/IKBa promoter represents a unique feature of this gene.