The human serotonin-4 (5-HT4) receptor gene expression is highly regulated in various tissues. We isolated the human 5-HT4 receptor gene containing the 5'-flanking region and characterized its promoter. By 5'-RACE (5'-rapid amplification of the cDNA ends) and inverse PCR, multiple transcription initiation sites were identified. The most 5' one (assigned to + 1) was 5135 bp upstream to the translation start site. The 500-bp 5'-flanking region contained potential binding sites for transcription factor Sp-1, AP-2, AP-4, and GATA. However, this region lacked TATA- and CAAT-boxes. Transient transfection analyses in human choriocarcinoma T3M-3 (5-HT4 receptor-positive) and HepG2 (5-HT4 receptor-negative) cells revealed that the region (-210 to -105) is necessary for the basic and cell-type specific 5-HT4 receptor gene expression. In addition, untranslated exon 1 contained negative (+ 112 to + 182) as well as positive (+ 1 to + 111) modulators, indicating that exon I plays a regulatory role in the 5-HT4 receptor gene expression. (C) 2001 Elsevier Science.