Analysis of DNase I-hypersensitive sites in the chromatin of the chicken adenosine receptor 2B gene reveals multiple cell-type-specific cis-regulatory elements.

We have cloned and sequenced the gene encoding the chicken A2B adenosine receptor, a member of the family of G-protein-coupled seven-transmembrane-domain receptors which is activated by extracellular adenosine. The gene occupies about 10 kb of genomic sequences and contains two exons. The promoter of the gene is associated with a CpG-rich island and lacks a canonical TATA-box. Previous work has shown that the chicken A2B adenosine receptor is a direct target gene of the transcription factors v-Myb and c-Myb and that its expression in the hematopoietic system is specific for myelomonocytic as well as erythroid cells. To understand the molecular basis of this cell type specificity we have searched for cis-regulatory DNA elements that direct the expression of the gene to specific hematopoietic lineages. As a first step towards this aim we have mapped DNase I-hypersensitive sites in the chromatin of the A2B adenosine receptor gene. Our studies reveal multiple nuclease-sensitive sites which are located in the intron of the gene and in the upstream region. A number of these sites are cell-type-specific suggesting that they correspond to cell-type-specific cis-regulatory DNA elements. To characterize the possible function of these elements we have performed reporter gene studies. Our results show that several of the nuclease-sensitive regions act as myelomonocytic-specific cis-acting stimulatory elements. Taken together, our data suggest that the expression of the A2B adenosine receptor gene in myelomonocytic cells is controlled by multiple cell type-specific cis-acting sequences located upstream and within the intron of the gene.