A CELL-TYPE-SPECIFIC ENHANCER IN THE HUMAN B7.1 GENE REGULATED BY NF-KAPPA-B

The costimulatory molecule B7.1 provides a second signal critical for T cell activation. The distribution of this integral membrane protein is restricted to certain tissues where its level of expression is modu lated by multiple exogenous stimuli. To identify the molecular basis f or specificity and inducibility, the chromatin cofiguration of the hum an B7.1 gene was examined in intact nuclei from various cell types. Th e identification of a tissue-specific deoxyribonuclease I hypersensiti ve site similar to 3kb upstream of the transcription start site led to the characterization of a cell type-specific enhancer region. This 18 3-bp region was both cell type specific and responsive to two distinct stimuli, lipopolysaccharide and dibutyryl cAMP, known to regulate B7. 1 expression. Deletional and site-directed mutagenesis revealed the pr esence of multiple functionally critical cis elements within this regi on, one of which was a nuclear factor (NF)-kappa B consensus sequence. In B7.1-positive B cells, this element bound several members of the N F-kappa B family, transcription factors already implicated in signal t ransduction pathways relevant to B7.1 expression. This is the first de scription, to our knowledge, of regulatory elements that control expre ssion of a gene encoding a B7 costimulatory molecule.