The levels of alcohol metabolizing enzymes could determine the rate of alcohol metabolism, which in turn plays an important role in the susceptibility to alcohol dependence. To understand the transcriptional regulation of the human ADH genes, we sought to identify distal regulatory elements in the ADH cluster. In this study we discovered a strong enhancer, 4E3, between the ADH4 and ADH6 genes. 4E3, located 13 kb upstream of the ADH4 translational start site, increased the activity of its cognate ADH4 promoter 50-fold in a human hepatoma cell line (HepG2). It also enhanced the activity of another strong promoter, SV40 promoter, 56-fold. The weakest promoter tested, ADH1B, was enhanced 180-fold. Because it functions on these heterologous promoters, we believe that in the absence of intervening boundary elements this enhancer would also act on the ADH6 promoter 60 kb away. The 4E3 enhancer was not functional in a non-hepatic cell line, H1299 lung carcinoma cells, suggesting that it has cell-type specificity.
