Promoters of the mammalian class III alcohol dehydrogenase genes

The ontogeny, distribution, and regulation of alcohol dehydrogenase 3: implications for pulmonary physiology

Class III alcohol dehydrogenase (ADH3), also termed formaldehyde dehydrogenase or S-nitrosoglutathione reductase, plays a critical role in the enzymatic oxidation of formaldehyde and reduction of nitrosothiols that regulate bronchial tone. Considering reported associations between formaldehyde vapor exposure and childhood asthma risk, and thus potential involvement of ADH3, we reviewed the ontogeny, distribution, and regulation of mammalian ADH3. Recent studies indicate that multiple biological and chemical stimuli influence expression and activity of ADH3, including the feedback regulation of nitrosothiol metabolism. The levels of ADH3 correlate with, and potentially influence, bronchial tone; however, data gaps remain with respect to the expression of ADH3 during postnatal and early childhood development. Consideration of ADH3 function relative to the respiratory effects of formaldehyde, as well as to other chemical and biological exposures that might act in an additive or synergistic manner with formaldehyde, might be critical to gain better insight into the association between formaldehyde exposure and childhood asthma.

Regulation of the mammalian alcohol dehydrogenase genes

This review focuses on the regulation of the mammalian medium-chain alcohol dehydrogenase (ADH) genes. This family of genes encodes enzymes involved in the reversible oxidation of alcohols to aldehydes. Interest in these enzymes is increased because of their role in the metabolism of beverage alcohol as well as retinol, and their influence on the risk for alcoholism. There are six known classes ADH genes that evolved from a common ancestor. ADH genes differ in their patterns of expression: most are expressed in overlapping tissue-specific patterns, but class III ADH genes are expressed ubiquitously. All have proximal promoters with multiple cis-acting elements. These elements, and the transcription factors that can interact with them, are being defined. Subtle differences in sequence can affect affinity for these factors, and thereby influence the expression of the genes. This provides an interesting system in which to examine the evolution of tissue specificity. Among transcription factors that are important in multiple members of this gene family are the C/EBPs, Sp1,USF, and AP1, HNF-1, CTF/NF-1, glucocorticoid, and retinoic acid receptors, and several as-yet unidentified negative elements, are important in at least one of the genes. There is evidence that cis-acting elements located far from the proximal promoter are necessary for proper expression. Three of the genes have upstream AUGs in the 5' nontranslated regions of their mRNA, unusual for mammalian genes. The upstream AUGs have been shown to significantly affect expression of the human ADH5 gene.

Histological distribution of class III alcohol dehydrogenase in human brain

The distributions of class III alcohol dehydrogenase (ADH), a glutathione-dependent formaldehyde dehydrogenase, and class I ADH in the human brain were examined immunohistochemically. The most intense immunostaining of class III ADH was observed in the dendrites and cytoplasm of cerebellar Purkinje cells. Scattered cerebral cortical neurons in layers IV and V, and some hippocampal pyramidal neurons were also immunopositive. The neuronal distribution of class III ADH resembled that of the vulnerable neurons in patients with hypoxic encephalopathy, which in view of the intense staining in the Purkinje cells, raises the possibility that this enzyme contributes to the hypoxia and cerebellar degeneration suffered by chronic alcoholics. Perivascular and subependymal astrocytes, which contribute to the maintenance of the cerebral cellular milieu and isolate the brain from the systemic circulation and cerebrospinal fluid, were also class III ADH positive. As the substrates of this enzyme include intrinsic toxic formaldehyde, inflammatory intermediate of 20-hydroxy-leukoteiene B4, and possibly ethanol, the distribution of class III ADH immunostaining indicates this enzyme contributes to the defence of the brain against degenerative processes. The finding that, unlike ependymal cells, subependymal astrocytes were class III ADH positive, suggests this enzyme may be useful for differentiating astrocytes and ependymal cells.

Characterization of the functional gene encoding mouse class III alcohol dehydrogenase (glutathione-dependent formaldehyde dehydrogenase) and an unexpressed processed pseudogene with an intact open reading frame

Multiple forms of vertebrate alcohol dehydrogenase (ADH) have been identified, but only one form, class III ADH, has been conserved in all organisms studied. Class III ADH functions in vitro as a glutathione-dependent formaldehyde dehydrogenase, which suggests that this was the original function that drove the evolution of ADH. Genetic analysis of class III ADH in yeast supports this view, but such studies are lacking in higher eukaryotes. The mouse ADH family has been previously analyzed and it contains three forms of ADH including the class III enzyme. We have initiated a molecular genetic analysis of the mouse class III ADH gene (Adh-2) by screening a genomic library with a full-length cDNA. Two overlapping clones contained the complete Adh-2 gene composed of nine exons in a 12-kb region, with the placement of introns matching that observed in other mammalian ADH genes. In this screening, we also isolated a clone (psi Adh-2) that lacks introns and which resembles a processed pseudogene. psi Adh-2 contained 25 point mutations relative to the previously analyzed Adh-2 cDNA, but still retained an intact open reading frame. Northern blot analysis using gene-specific probes provided evidence that psi Adh-2 does not produce a mRNA in either liver or kidney, whereas Adh-2 does. The functionality of the two genes was also compared by fusion of their 5'-flanking regions to a lacZ reporter gene. Reporter gene expression following transfection into mouse F9 embryonal carcinoma cells indicated that only Adh-2 possesses promoter activity.