NF-κB/Rel family members regulating the ICAM-1 promoter in monocytic THP-1 cells

A kappa B-site nas identified in the promoter of the intercellular adhesion molecule-1 (ICAM-1) gene, which is involved in regulation of ICAM-1 expression by tumor necrosis factor alpha (TNF-alpha) and glucocorticoids, We now report on the transcription factors which bind and transactivate this enhancer sequence. In vitro, the ICAM-I kappa B site appealed to bind RelA and c-Rel homodimers as well as heterodimers with NF-kappa B1, but weakly NF-kappa B1 homodimers. In addition, both RelA and c-Rel, but nor NF-kappa B1, were shown to transactivate an ICAM-1 kappa B-repurter construct. In monocytic THP-1 cells TNF-alpha induced two nuclear complexes which in vitro bound to the ICAM-1 kappa B site. Using antibodies in an electrophoretic mobility supershift assay, one of these complexes was shown to contain NF-kappa B1 and RelA, and to bind with higher affinity to the consensus KB site in the HIV long terminal repeat. The second complex contained RelA, and exhibited higher affinity towards the ICAM-1 kappa B than to the HIV kappa B site. The glucocorticoid corticoid receptor was shown to repress activity of both the RelA homodimer and the NF-kappa B1/RelA heterodimer. We argue that in vivo RelA homodimers are likely to play a dominant role in TNF-alpha-induced ICAM-1 transcription in monocytic cells.