TATA‐Driven Transcriptional Initiation and Regulation of the Rat Serotonin 5‐HT 1A Receptor Gene

The transcriptional initiation and regulation of the ratserotonin 5‐HT 1A receptor gene were characterized. By three typesof analyses, a single brain‐specific site of transcriptional initiation waslocalized to ‐967 bp upstream of the translation initiation condon that isutilized both in hippocampus and in the rat raphe RN46A cell line. This majorsite of transcriptional initiation was located 58 bp downstream from aconsensus TATA element, suggesting TATA‐driven transcription of the rat5‐HT 1A receptor. To identify the promoter activity of the receptorgene, progressive 5′ deletions of the ‐2,719/‐117‐bp fragment of the5‐HT 1A promoter linked to luciferase gene were transfected into5‐HT 1A ‐negative (pituitary GH4C1, L6 myoblast, and C6 glioma) and5‐HT 1A ‐positive (septal SN‐48 and raphe RN46A) cell lines. Enhancerregions were identified within a fragment between nucleotides ‐426 and ‐117that selectively enhanced transcription in 5‐HT 1A ‐positive cells. Anonselective enhancer/promoter that mediated expression in all cell lines waslocated upstream between ‐1,519 and ‐426 bp in a DNA segment containingconsensus TATA, CCAAT, SP‐1, and AP‐1 elements as well as apoly‐GT 26 dinucleotide repeat. Strong repression of transcriptionin all cell lines was conferred by the region upstream of ‐1,519 bp thatcontains a 152‐bp DNA segment with >80% identity to RANTES, tumor necrosisfactor‐β, and other immune system genes. Our results indicate thatTATA‐driven expression of the 5‐HT 1A receptor is regulated by a novel proximal tissue‐specific enhancer region, a nonselective promoter, and an upstream repressor region that is distinct from previously identified neuron‐specific repressors.