IDENTIFICATION OF A PROMOTER ELEMENT THAT REGULATES TISSUE-SPECIFIC EXPRESSION OF THE HUMAN CD80 (B7.1) GENE

We isolated the promoter region of the gene encoding human CD80 to exa mine for elements responsible for the regulated expression of this imp ortant costimulatory molecule, Using CAT reporter constructs containin g a heterologous general enhancer, we demonstrate that the CD80 promot er is active in CD80-expressing Raji cells, but has no significant act ivity in jurkat cells that are CD80 negative, Transcriptional activity in Raji increases as the promoter is truncated from nucleotide positi on -906 to -84. However, truncation of this promoter to -41 significan tly decreases its activity, Within this region is one stretch of DNA t hat is protected in DNase I footprint analysis and that shows some seq uence similarity to the NF-kappa B element. Site-specific mutation of the 5' purine-rich portion of this element (B7-RE, or B7 regulatory el ement) abrogates expression. Nuclear extracts prepared from Raji, or f rom leukemic cells induced to express CD80, form a distinct complex(es ) with B7-RE in electromobility shift assays. Moreover, a consensus NF -kappa B oligonucleotide can compete with B7-RE for nuclear extract bi nding However, no super-shifted bands are observed when extracts are p reincubated with Abs to p50, p65, or other Rel proteins. Moreover, we find that recombinant p49 (RelB), p50, p65 (RelA), or p49/p65 heterodi mers do not bind B7-RE in vitro, These data indicate that B7-RE may he lp govern expression of genes independent of a tissue-specific enhance r and that this element is bound by nuclear factor(s) other than those that commonly bind NF-kappa B.