Identification of a FOXA-dependent enhancer of human alcohol dehydrogenase 4 (ADH4)

Human alcohol dehydrogenase 4 (ADH4) is one of the key enzymes involved in the metabolism of alcohol. ADH4 is highly expressed in the liver, and previous studies have revealed several cis-acting elements in the proximal promoter region. In this study we have identified a distal upstream enhancer, 4E, of ADH4. In HepG2 human hepatoma cells, 4E increased the activity of an ADH4 basal promoter by 50-fold. 4E was cell-specific, as no enhancer activity was detected in a human lung cell line, H1299. We have narrowed the enhancer activity to a 565 bp region and have identified multiple liver-enriched transcription factor binding sites in the region. By electrophoretic mobility shift assays, we confirmed binding of FOXA proteins to these sites. Site-directed mutagenesis studies demonstrated that sites 1 and 4 have the biggest effect on enhancer function, and mutations in multiple sites have multiplicative effects. We also studied the effects of three variations in the minimal enhancer region. Two variations had a significant effect on enhancer activity, decreasing the activity to 0.6-fold, while one had small but significant effect. The differences in the functional activity in different haplotypes suggest that this region could play an important role in the risk for alcoholism.