The basal promoter activity of the human AT1 receptor gene was characterized using a human hepatoma cell line with a considerably high expression of AT1, PLC-PRF-5. Four cis-acting, positively regulating elements termed AT1PRE1 (-113 to -102 bp), AT1PRE2 (-49 to -43 bp), AT1PRE3 (-5 to -2 bp) and AT1PRE4 (+44 to +50 bp) were identified. AT1PRE2 contained a GC-box-like sequence and bound to Sp1. AT1PRE1 contained two tandem GC-boxes and was bound to several nuclear proteins in addition to Sp1. Nuclear proteins that were bound sequence-specifically to AT1PRE1, AT1PRE2 and AT 1PRE4 were found in both PLC-PRF-5 cells and 8505C cells, while those bound to AT1PRE3 were not found in 8505C cells, which showed no expression of AT1 and almost no promoter activity for the AT 1 gene. Significant promoter activity was still observed even when AT1PRE1, AT1PRE2 and AT1PRE4 were all mutated. Mutagenesis of AT1PRE3, however, substantially inactivated promoter activity. AT1PRE1, AT1PRE2 and AT1PRE4 synergistically enhanced AT1 gene transcription promoted by AT 1PRE3. These results suggested that AT1PRE3 is responsible for the tissue-specific expression of the human AT1 gene, and that AT1PRE1, AT1PRE2 and AT1PRE4 function as a general enhancer in liver-derived cells.
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