The genomic structure and transcriptional regulation of the rat apelin receptor (APJR) were analysed by rapid amplification of 5' cDNA ends (5'-RACE), transient expression assays and DNA-protein interaction. Analysis of the 5'-flanking region of a rat genomic clone shows no TATA box, but a putative CAAT box and several putative binding sites for transcription factors are present. Two transcriptional start sites were identified by 5'-RACE, RNase protection and primer extension analyses. Promoter activity was exhibited in the APJR- expressing SH-SY5Y cell line as well as in COS-7 and Chinese hamster ovary (CHO-K1) cells. Consecutive 5'-deletion analysis revealed the highest promoter activity in a region between bp -966 and -165. DNaseI footprint analysis revealed seven protected regions and electrophoretic mobility shift, super-shift and competition assays identified individual DNA-protein complexes capable of binding Sp1, estrogen receptor (ER)alpha, glucocorticoid receptor and CCAAT enhancer binding protein (C/EBP)gamma transcription factors. Site-directed mutagenesis identified an individual Sp1 motif that plays a major role in activation of the APJR promoter and also demonstrated constitutive transcriptional regulation of the promoter by estrogen and glucocorticoid receptors. Promoter regulation by the cAMP-dependent signal cascade was also shown.