Indiana University-Purdue University Indianapolis (IUPUI) / Alcohol dehydrogenase (ADH) genes encode proteins that metabolize ethanol to acetaldehyde. Humans have seven ADH genes in a cluster. The hypothesis of this study was that by controlling the levels of ADH enzymes, cis-regulatory regions could affect the risk for alcoholism. The goal was thus to identify distal regulatory regions of ADHs. To achieve this, sequence conservation across 220 kb of the ADH cluster was examined. An enhancer (4E) was identified upstream 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. The enhancer activity was located in a 565 bp region (4E3). Four FOXA and one HNF-1A protein binding sites were shown to be functional in the 4E3 region. To test if this region could affect the risk for alcoholism, the effect of variations in 4E3 on enhancer activity was tested. Two variations had a significant effect on enhancer activity, decreasing the activity to 0.6-fold. A third variation had a small but significant effect. The effect of variations in the ADH1B proximal promoter was also tested. At SNP rs1229982, the C allele had 30% lower activity than the A allele. In addition to studying the regulatory regions of ADH genes, the effects of alcohol on liver-derived cells (HepG2) were also explored. Liver is the primary site of alcohol metabolism, and is highly vulnerable to injuries due to chronic alcohol abuse. To identify the effects of long term ethanol exposure on global gene expression and alternative splicing, HepG2 cells were cultured in 75 mM ethanol for nine days. Global gene expression changes and alternative splicing were measured using Affymetrix GeneChip® Human Exon 1.0 ST Arrays. At the level of gene expression, genes involved in stress response pathways, metabolic pathways (including carbohydrate and lipid metabolism) and chromatin regulation were affected. Alcohol effects were also observed on alternative transcript isoforms of some genes.

Indiana University-Purdue University Indianapolis (IUPUI) / Seven human alcohol dehydrogenase genes (which encode the primary enzymes involved in alcohol metabolism) are grouped into classes based on function and sequence identity. While the Class I ADH isoenzymes contribute significantly to ethanol metabolism in the liver, Class IV ADH isoenzymes are involved in the first-pass metabolism of ethanol. It has been suggested that the ability to efficiently oxidize ethanol occurred late in primate evolution. Kinetic data obtained from the Class I ADH isoenzymes of marmoset and brown lemur, in addition to data from resurrected ancestral human Class IV ADH isoenzymes, supports this proposal--suggesting that two major events which occurred during primate evolution resulted in major adaptations toward ethanol metabolism. First, while human Class IV ADH first appeared 520 million years ago, a major adaptation to ethanol occurred very recently (approximately 15 million years ago); which was caused by a single amino acid change (A294V). This change increases the catalytic efficiency of the human Class IV enzymes toward ethanol by over 79-fold. Secondly, the Class I ADH form developed 80 million years ago--when angiosperms first began to produce fleshy fruits whose sugars are fermented to ethanol by yeasts. This was followed by the duplication and divergence of distinct Class I ADH isoforms--which occurred during mammalian radiation. This duplication event was followed by a second duplication/divergence event which occurred around or just before the emergence of prosimians (some 40 million years ago). We examined the multiple Class I isoforms from species with distinct dietary preferences (lemur and marmoset) in an effort to correlate diets rich in fermentable fruits with increased catalytic capacity toward ethanol oxidation. Our kinetic data support this hypothesis in that the species with a high content of fermentable fruit in its diet possess greater catalytic capacity toward ethanol.