Analysis of an alternative promoter that regulates tissue-specific expression of the human aromatic L-amino acid decarboxylase gene in cultured cell lines

The human aromatic L-amino acid decarboxylase (AADC) gene is transcribed in a tissue-specific manner by an alternative promoter. In this study using human cultured cell lines, we analyzed the alternative promoter that regulates tissue-specific expression of AADC. Neither neuronalnor nonneuronal-type mRNA of AADC was detected in HeLa cells, nonneuronal-type mRNA of AADC was expressed in HepG2 cells, and the neuronal-type was expressed in the SK-N-SH cell line. We examined the promoter activities located in 5′- and 3′-fianking regions of exon Nl and exon LI by transfection experiments. Plasmids containing 5′-flanking regions of exon LI, the shortest of which was 0.3kb, could promote specifically high expression of the reporter gene in HepG2 cells. On the other hand, plasmids containing 5'-flanking regions of exon Nl (3.6 kb to 0.5 kb) could promote the reporter gene expression not only in SK-N-SH cells but also in HeLa and HepG2. More enhanced expression were observed by transfection of plasmids containing parts of the first intron in these cell lines. Thus, these results suggest that the basal liver-specific promoter activity is located in the 5′-flanking region of exon LI and that the first intron may also be needed for enhanced expression rather than determination of cell-specificity.