Transcription of the rat dopamine-D2-receptor gene from two promoters

Modulation of the expression of the D2-dopamine receptor gene is involved in several pathological and developmental circumstances. The gene and the corresponding promoter regions of the rat D2 receptor were isolated and partly characterized to study its regulation. The rat D2-receptor gene spans at least 50 kb, and possesses eight exons; its organization was compared to those of the other dopamine-receptor genes in a phylogenetic perspective. The gene contains two transcription-start sites: the major one is located about 320 bp upstream from the 3' end of the first exon, and a minor site is 70 bp further upstream. Transient-expression assays with fusion constructs comprising fragments of the D2-promoter region and the luciferase reporter gene confirmed the existence of two independent, TATA-lacking promoters. Both promoters separately induced transcription of the luciferase gene in C6 glioma, primary fibroblasts, GH3 and MMQ pituitary cell lines, among which only the MMQ cells normally express the D2 receptor. Transcription is enhanced by the reunion of the two promoters, and modified by the addition of upstream sequences. Thus the 1-kb promoter region analysed does not contain all the elements necessary to confer tissue-specific expression of the gene, but does carry some positive and negative regulatory elements, which remain to be characterized.