Human act and AR1 sequences differentially regulate murine and human D1A dopamine receptor promoters

The D1A dopamine receptor gene underlies complex transcriptional regulation in order to achieve the tissue-specific expression. Transcription in the D1A genes proceeds from two distinct promoters utilized for the tissue-specific regulation of these genes. Furthermore, analysis of the human D1A dopamine receptor gene has revealed that the region between nucleotides -1173 and -1136 (ActAR1) of the gene might be important for its neural cell-specific expression. To investigate the function of D1A dopamine receptor promoters in the brain cell-specific expression of transgenes, we analyzed the regulatory patterns of two distinct protein-binding regions of ActAR1, i.e., an Act sequence (-1174/-1154) and an AR1 sequence (-1154/-1136), toward murine and human D1A promoters. Transient expression analyses using various chloramphenicol acetyltransferase constructs revealed that Act could not activate murine or human D1A promoters, and that AR1 could effectively stimulate these promoters in a cell type-non-specific manner. Only ActAR1, a combination of Act and AR1, could activate murine and human D1A promoters in a prominent cell type-specific manner. Abundant protein binding to Act was detected by gel mobility shift assay using nuclear extracts from SK-N-MC, NS20Y, OK, and C6 but faint protein binding using nuclear extracts from HepG2. Furthermore, strong protein binding to AR1 was detected using nuclear extracts from SK-N-MC, NS20Y, HepG2 but faint protein binding from C6 extracts and no detectable protein binding from OK extracts. These observations suggest that the tissue-specific expression of the D1A gene is due, at least in part, to the differential expression of these activator proteins that bind to Act and AR1.