Tissue-specific promoter usage in the D(1A) dopamine receptor gene in brain and kidney

The D(1A) dopamine receptor gene consists of a short, noncoding exon 1 separated from a longer coding exon 2 by a small intron. Recently, we found that in addition to its original TATA-less promoter located upstream of exon 1, the human D(1A) dopamine receptor gene is transcribed in neural cells from a second strong promoter located in its intron. In the present study, we addressed the possibility that these two promoters are used for the tissue- specific regulation of the D(1A) gene in neuronal and renal cells. Reverse transcription polymerase chain reaction revealed that D(1A) transcripts in the kidneys of humans and rats lack exon 1. Transient transfection analysis of these two promoters in D(1A)-expressing cells indicated that the upstream promoter has no detectable activity in the opossum kidney (OK) cell line, in contrast to its strong activity in two neuronal cell lines, SK-N-MC and NS20Y. On the other hand, the D(1A) intron promoter showed transcriptional activity both in OK cells and in neuronal cells. The activator sequence AR1, which enhances transcription from the upstream promoter in SK-N-MC and NS20Y cells, could not activate this promoter in OK cells. In addition, no protein binding to AR1 could be detected by gel mobility shift assay using nuclear extracts from either OK cells or from rat kidney tissue. These findings indicate that the differential expression of short and long D(1A) transcripts is due, at least in part, to the tissue-specific expression of the activator protein binding to AR1 driving transcription from the upstream promoter. Absence of this activator protein accounts for the nonfunctional D(1A) upstream promoter in the kidney.