An upstream protein interacts with a distinct protein that binds to the cap site of the human interleukin 1 beta gene

Interleukin 1 beta (IL-1 beta) is a proinflammatory cytokine that exhibits a wide variety of biological activities. Genomic sequences that mediate the induction of human IL-1 beta gene transcription by lipopolysaccharide and phorbol esters are located more than 2,700 bp upstream of the transcriptional start site (cap site). These upstream elements require additional cap site-proximal (CSP) sequences which are necessary for basal transcription of the human IL-1 beta gene. In addition, these CSP sequences have been shown to mediate both cell type-specific expression of this gene, and trans-activation by some viral proteins. In this study, we report the identification of a novel nuclear protein, termed NF beta C, that binds to a DNA sequence which spans the cap site of the human IL-1 beta gene (positions -12 to +8). We have also identified a second region (positions -305 to -280) containing a putative NF-kappa B binding site. We show here that this region can bind three distinct nuclear proteins. One protein is similar or identical to NF-kappa B, a second protein (termed NF beta B) binds a distinct sequence that substantially overlaps the 5' half of the NF kappa B binding sequence, and a third protein (termed NF beta D) binds a distinct sequence that substantially overlaps the 3' half of the NF kappa B binding sequence. Unlike NF kappa B, NF1 beta B and NF beta D are present in nuclear extracts prepared from unstimulated monocytic cells. Although the NF beta D and NF beta C binding sequences share no significant similarity, each sequence can specifically compete for the binding of either protein to DNA, whereas oligonucleotides containing only the NF kappa B or NF beta B motifs do not compete for the binding of NF beta C or NF beta D. This suggests that NF beta C and NF beta D can specifically interact in vitro, possibly through a common subunit.