Genomic structure and expression of the ADH7 gene encoding human class IV alcohol dehydrogenase, the form most efficient for retinol metabolism in vitro

Neuroblastoma in relation to joint effects of vitamin A and maternal and offspring variants in vitamin A-related genes: A report of the Children's Oncology Group

BACKGROUND

There is evidence vitamin A plays a role in neuroblastoma. Not only is 13-cis-retinoic acid used as maintenance therapy for high-risk cases, but prenatal vitamin intake use may decrease neuroblastoma risk. We hypothesized that single nucleotide polymorphisms (SNPs) in vitamin A-related genes are may be associated with neuroblastoma risk and potentially be modified by vitamin A intake.

METHODS

The Neuroblastoma Epidemiology in North America (NENA) study recruited 563 case-parent sets through the Children's Oncology Group's Childhood Cancer Research Network. We ascertained dietary nutrient intake through questionnaires and genotyped 463 SNPs in vitamin A-related genes from saliva DNA. Offspring and maternal log-additive risk ratios (RR) and stratum-specific RR for gene-environment interaction were estimated with a log-linear model. We avoided false positives due to multiple testing by using the false discovery rate (FDR).

RESULTS

When all neuroblastoma cases were considered together, no offspring variants met the significance criteria (FDR Q-value < 0.2). One maternal SNP (rs12442054) was associated with decreased risk of neuroblastoma (RR: 0.61; 95% Confidence Interval (CI): 0.47-0.79, Q = 0.076). When the cases were categorized according to prognostic risk category and age at onset, nine offspring SNPs were significantly associated with intermediate-risk neuroblastoma. Maternal rs6776706 was associated with (RR: 0.49; 95% CI: 0.33-0.72, Q = 0.161) high-risk neuroblastoma and maternal rs11103603 (RR: 0.60; 95% CI: 0.45-0.79, Q = 0.127) was associated with neuroblastoma aged <1 year. For gene-environment interaction, maternal rs729147 was associated with decreased risk of neuroblastoma among mothers with vitamin A consumption above the recommendation.

CONCLUSIONS

Although there is biologic plausibility for the role of vitamin A in neuroblastoma, we found weak evidence of a relationship between vitamin A related genes and neuroblastoma.

Alcohol consumption, variability in alcohol dehydrogenase genes and risk of renal cell carcinoma

Alcohol consumption has been associated inversely with renal cell carcinoma (RCC) risk; however, no study has examined effect modification by germline variation in alcohol-metabolizing genes. We investigated whether the association between alcohol intake and RCC risk is modulated by germline variants in alcohol dehydrogenase genes in a large case-control study. Data from 652 RCC cases and 1,366 non-cancer controls were analyzed. Alcohol intake was assessed using a standardized risk factor questionnaire. Three previously genotyped polymorphisms in ADH6 and ADH7 with the TaqMan assay were examined. Odds ratios (ORs) and 95% confidence interval (CI) were calculated using logistic regression, adjusting for covariates. Compared to non-drinkers, ever consumption of alcohol was associated with lower RCC risk (OR = 0.52, 95% CI = 0.42-0.65). Analysis with cubic spline regression curve showed a "J-shaped" relationship between alcohol drinks/day and RCC risk, such that there was no added benefit against RCC for consumption of more than two drinks/day. We observed effect modification by variation in rs1154454 (ADH7) (p_interaction  = 0.007); a per unit increase in alcohol drink/day was associated with 35% lower RCC risk among non-minor allele carriers, a 27% lower risk among those who carry one copy of the minor allele, but no association was observed among those with two copies of the minor allele. These findings indicate that alcohol consumption is associated with lower RCC risk. Consuming more than two drinks a day does not confer additional protection against RCC. The association between alcohol intake and RCC risk appears to be modulated by inter-individual germline variation in alcohol-metabolizing genes.

The potential mechanism of bursal-derived BP8 on B cell developments

The bursa of Fabricius, the key humoral immune organ unique to birds, is critical for B cell differentiation and antibody production. BP8 (AGHTKKAP) is a novel immunomodulatory peptide that regulates B-cell development. Gene microarray was used to investigate the mechanism of BP8 on B cell development. BP8 regulated expressions of 1,570 genes that were involved in retinol metabolism, the Wnt signaling pathway, MAPK pathway, Jak-Stat pathway, Notch signaling pathway, cytokine-cytokine receptor interaction, and Ca(2+) signals. Finally, BP8 triggered ADH7 and RDH10 expression, interacted with retinol binding protein, and regulated retinol uptake in vitro and vivo. These data reveal a bursal-derived multifunctional factor, BP8, as a novel biomaterial which is essential for the development of the immune system and represents an important linker between the B cell development and retinol metabolism. This study elucidates the mechanisms involved in humoral immune system and has implications in treating human diseases.

Alcohol consumption and lifetime change in cognitive ability: a gene × environment interaction study

Studies of the effect of alcohol consumption on cognitive ability are often confounded. One approach to avoid confounding is the Mendelian randomization design. Here, we used such a design to test the hypothesis that a genetic score for alcohol processing capacity moderates the association between alcohol consumption and lifetime change in cognitive ability. Members of the Lothian Birth Cohort 1936 completed the same test of intelligence at age 11 and 70 years. They were assessed for recent alcohol consumption in later life and genotyped for a set of four single-nucleotide polymorphisms in three alcohol dehydrogenase genes. These variants were unrelated to late-life cognition or to socioeconomic status. We found a significant gene × alcohol consumption interaction on lifetime cognitive change (p = 0.007). Individuals with higher genetic ability to process alcohol showed relative improvements in cognitive ability with more consumption, whereas those with low processing capacity showed a negative relationship between cognitive change and alcohol consumption with more consumption. The effect of alcohol consumption on cognitive change may thus depend on genetic differences in the ability to metabolize alcohol.

The Xenopus alcohol dehydrogenase gene family: characterization and comparative analysis incorporating amphibian and reptilian genomes

Background

The alcohol dehydrogenase (ADH) gene family uniquely illustrates the concept of enzymogenesis. In vertebrates, tandem duplications gave rise to a multiplicity of forms that have been classified in eight enzyme classes, according to primary structure and function. Some of these classes appear to be exclusive of particular organisms, such as the frog ADH8, a unique NADP⁺-dependent ADH enzyme. This work describes the ADH system of Xenopus, as a model organism, and explores the first amphibian and reptilian genomes released in order to contribute towards a better knowledge of the vertebrate ADH gene family.

Results

Xenopus cDNA and genomic sequences along with expressed sequence tags (ESTs) were used in phylogenetic analyses and structure-function correlations of amphibian ADHs. Novel ADH sequences identified in the genomes of Anolis carolinensis (anole lizard) and Pelodiscus sinensis (turtle) were also included in these studies. Tissue and stage-specific libraries provided expression data, which has been supported by mRNA detection in Xenopus laevis tissues and regulatory elements in promoter regions. Exon-intron boundaries, position and orientation of ADH genes were deduced from the amphibian and reptilian genome assemblies, thus revealing syntenic regions and gene rearrangements with respect to the human genome. Our results reveal the high complexity of the ADH system in amphibians, with eleven genes, coding for seven enzyme classes in Xenopus tropicalis. Frogs possess the amphibian-specific ADH8 and the novel ADH1-derived forms ADH9 and ADH10. In addition, they exhibit ADH1, ADH2, ADH3 and ADH7, also present in reptiles and birds. Class-specific signatures have been assigned to ADH7, and ancestral ADH2 is predicted to be a mixed-class as the ostrich enzyme, structurally close to mammalian ADH2 but with class-I kinetic properties. Remarkably, many ADH1 and ADH7 forms are observed in the lizard, probably due to lineage-specific duplications. ADH4 is not present in amphibians and reptiles.

Conclusions

The study of the ancient forms of ADH2 and ADH7 sheds new light on the evolution of the vertebrate ADH system, whereas the special features showed by the novel forms point to the acquisition of new functions following the ADH gene family expansion which occurred in amphibians.

Fetal alcohol exposure and IQ at age 8: evidence from a population-based birth-cohort study

Background

Observational studies have generated conflicting evidence on the effects of moderate maternal alcohol consumption during pregnancy on offspring cognition mainly reflecting problems of confounding. Among mothers who drink during pregnancy fetal alcohol exposure is influenced not only by mother’s intake but also by genetic variants carried by both the mother and the fetus. Associations between children’s cognitive function and both maternal and child genotype at these loci can shed light on the effects of maternal alcohol consumption on offspring cognitive development.

Methods

We used a large population based study of women recruited during pregnancy to determine whether genetic variants in alcohol metabolising genes in this cohort of women and their children were related to the child’s cognitive score (measured by the Weschler Intelligence Scale) at age 8.

Findings

We found that four genetic variants in alcohol metabolising genes in 4167 children were strongly related to lower IQ at age 8, as was a risk allele score based on these 4 variants. This effect was only seen amongst the offspring of mothers who were moderate drinkers (1–6 units alcohol per week during pregnancy (per allele effect estimates were −1.80 (95% CI = −2.63 to −0.97) p = 0.00002, with no effect among children whose mothers abstained during pregnancy (0.16 (95%CI = −1.05 to 1.36) p = 0.80), p-value for interaction  = 0.009). A further genetic variant associated with alcohol metabolism in mothers was associated with their child’s IQ, but again only among mothers who drank during pregnancy.

Tissue-specific mRNA expression profiles of human phase I metabolizing enzymes except for cytochrome P450 and phase II metabolizing enzymes

Pairs of forward and reverse primers and TaqMan probes specific to each of 52 human phase I metabolizing enzymes (alcohol dehydrogenase, aldehyde dehydrogenase, aldehyde oxidase, dihydropyrimidine dehydrogenase, epoxide hydrolase, esterase, flavin-containing monooxygenase, monoamine oxidase, prostaglandin endoperoxide synthase, quinone oxidoreductase, and xanthene dehydrogenase) and 48 human phase II metabolizing enzymes (acetyltransferase, acyl-CoA:amino acid N-acyltransferase, UDP-glucuronosyltransferase, glutathione S-transferase, methyltransferase, and sulfotransferase) were prepared. The mRNA expression level of each target enzyme was analyzed in total RNA from single and pooled specimens of various human tissues (adrenal gland, bone marrow, brain, colon, heart, kidney, liver, lung, pancreas, peripheral leukocytes, placenta, prostate, salivary gland, skeletal muscle, small intestine, spinal cord, spleen, stomach, testis, thymus, thyroid gland, trachea, and uterus) by real-time reverse transcription PCR using an ABI PRISM 7700 Sequence Detection System. Further, individual differences in the mRNA expression of representative human phase I and II metabolizing enzymes in the liver were also evaluated. The mRNA expression profiles of the above phase I and phase II metabolizing enzymes in 23 different human tissues were used to identify the tissues exhibiting high transcriptional activity for these enzymes. These results are expected to be valuable in establishing drug metabolism-mediated screening systems for new chemical entities in new drug development and in research concerning the clinical diagnosis of disease.

Identification of new single nucleotid polymorphisms (SNP) in alcohol dehydrogenase class IV ADH7 gene within a French population

Many epidemiological studies have explored the possible link between the susceptibility to alcohol related cancers, such as oesophageal cancers, and genetic variants of alcohol dehydrogenases (ADHs). Alcohol dehydrogenase class IV ADH7 is mainly expressed in the upper aero-digestive tract and is involved in the first pass ethanol metabolism. As far as we know, no study has described single nucleotide polymorphisms (SNPs) within ADH7 exons in the Caucasian population. Therefore, in a pilot study, we used the denaturing high performance liquid chromatography (DHPLC) method to screen 49 oesophageal cancer cases for SNPs in the ADH7 gene. A total of 5 SNPs was observed in this study: one SNP in the 5' non-translated regions of exon 1, two SNPs in introns 3 and 4 and two others SNPs in exons 3 and 4. The SNP located in the exon 1, which has never been described before, occurred in a reverse TATA box whereas the SNP of exon 3 was a non-silent polymorphism. Because these two SNPs could potentially affect the transcription and/or the enzyme activity, their distribution was evaluated in a representative sample of healthy Caucasians (n = 89) recruited in Lower Normandy. Frequencies of heterozygous samples ranged from 11% (exon 3) to 28% (exon 1). No homozygous samples were found. In this pilot study, the DHPLC method was suitable for both SNP screening and genotyping and allowed the detection of five SNPs in the ADH7 gene, two of which have never been described before, among the European population.

Diplotype trend regression analysis of the ADH gene cluster and the ALDH2 gene: multiple significant associations with alcohol dependence

The set of alcohol-metabolizing enzymes has considerable genetic and functional complexity. The relationships between some alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) genes and alcohol dependence (AD) have long been studied in many populations, but not comprehensively. In the present study, we genotyped 16 markers within the ADH gene cluster (including the ADH1A, ADH1B, ADH1C, ADH5, ADH6, and ADH7 genes), 4 markers within the ALDH2 gene, and 38 unlinked ancestry-informative markers in a case-control sample of 801 individuals. Associations between markers and disease were analyzed by a Hardy-Weinberg equilibrium (HWE) test, a conventional case-control comparison, a structured association analysis, and a novel diplotype trend regression (DTR) analysis. Finally, the disease alleles were fine mapped by a Hardy-Weinberg disequilibrium (HWD) measure (J). All markers were found to be in HWE in controls, but some markers showed HWD in cases. Genotypes of many markers were associated with AD. DTR analysis showed that ADH5 genotypes and diplotypes of ADH1A, ADH1B, ADH7, and ALDH2 were associated with AD in European Americans and/or African Americans. The risk-influencing alleles were fine mapped from among the markers studied and were found to coincide with some well-known functional variants. We demonstrated that DTR was more powerful than many other conventional association methods. We also found that several ADH genes and the ALDH2 gene were susceptibility loci for AD, and the associations were best explained by several independent risk genes.

Alcohol linked to enhanced angiogenesis in rat model of choroidal neovascularization

One of the pathologic complications of exudative (i.e. wet-type) age-related macular degeneration (AMD) is choroidal neovascularization (CNV). The aim of this study was to investigate whether chronic and heavy alcohol consumption influenced the development of CNV in a rat model. The oxidative metabolism of alcohol is minimal or absent in the eye, so that ethanol is metabolized via a nonoxidative pathway to form fatty acid ethyl esters (FAEE). Fatty acid ethyl ester synthase (FAEES) was purified from the choroid of Brown Norway (BN) rats. The purified protein was 60 kDa in size and the antibody raised against this protein showed a single band on western blot. BN rats on a regular diet were fed alcohol for 10 weeks. Control rats were fed water with a regular diet and pair-fed control rats were fed regular diet, water and glucose. We found that FAEES activity was increased 4.0-fold in the choroid of alcohol-treated rats compared with controls. The amount of ethyl esters produced in the choroid of 10 week alcohol-fed rats was 7.4-fold more than rats fed alcohol for 1 week. The increased accumulation of ethyl esters was associated with a 3.0-fold increased expression of cyclin E and cyclin E/CDK2; however, the level of the cyclin kinase inhibitor, p27Kip, did not change. The increased accumulation of ethyl esters was also associated with 3.0-fold decreased expression of APN in the choroid. We also found that the size of CNV increased by 28% in alcohol-fed rats. Thus, our study showed that chronic, heavy alcohol intake was associated with both an increased accumulation of ethyl esters in the choroid and an exacerbation of the CNV induced by laser treatment. These results may provide insight into the link between heavy alcohol consumption and exudative AMD.

Genetic time-series analysis identifies a major QTL for in vivo alcohol metabolism not predicted by in vitro studies of structural protein polymorphism at the ADH1B or ADH1C loci

After ingestion of a standardized dose of ethanol, alcohol concentrations were assessed, over 3.5 hours from blood (six readings) and breath (10 readings) in a sample of 412 MZ and DZ twins who took part in an Alcohol Challenge Twin Study (ACTS). Nearly all participants were subsequently genotyped on two polymorphic SNPs in the ADH1B and ADH1C loci known to affect in vitro ADH activity. In the DZ pairs, 14 microsatellite markers covering a 20.5 cM region on chromosome 4 that includes the ADH gene family were assessed, Variation in the timed series of autocorrelated blood and breath alcohol readings was studied using a bivariate simplex design. The contribution of a quantitative trait locus (QTL) or QTL's linked to the ADH region was estimated via a mixture of likelihoods weighted by identity-by-descent probabilities. The effects of allelic substitution at the ADH1B and ADH1C loci were estimated in the means part of the model simultaneously with the effects sex and age. There was a major contribution to variance in alcohol metabolism due to a QTL which accounted for about 64% of the additive genetic covariation common to both blood and breath alcohol readings at the first time point. No effects of the ADH1B*47His or ADH1C*349Ile alleles on in vivo metabolism were observed, although these have been shown to have major effects in vitro. This implies that there is a major determinant of variation for in vivo alcohol metabolism in the ADH region that is not accounted for by these polymorphisms. Earlier analyses of these data suggested that alcohol metabolism is related to drinking behavior and imply that this QTL may be protective against alcohol dependence.

Frequencies of single nucleotide polymorphism in alcohol dehydrogenase7 gene in patients with multiple system atrophy and controls

A polymerase chain reaction and direct sequencing of the ADH7 gene were carried out in 50 controls and 50 patients with probable multiple system atrophy (MSA). Seven SNPs, one insertion, and one mismatch were found in patients with MSA and controls. There was no significant difference in the frequencies of each SNP between the patients and the controls (P > 0.05). Interpretation of this negative finding should be cautious in view of the relatively small number of cases.

Distribution of class I, III and IV alcohol dehydrogenase mRNAs in the adult rat, mouse and human brain

The localization of different classes of alcohol dehydrogenases (ADH) in the brain is of great interest because of their role in both ethanol and retinoic acid metabolism. Conflicting data have been reported in the literature. By Northern blot and enzyme activity analyses only class III ADH has been detected in adult brain specimens, while results from riboprobe in situ hybridization indicate class I as well as class IV ADH expression in different regions of the rat brain. Here we have studied the expression patterns of three ADH classes in adult rat, mouse and human tissues using radioactive oligonucleotide in situ hybridization. Specificity of probes was tested on liver and stomach control tissue, as well as tissue from class IV ADH knock-out mice. Only class III ADH mRNA was found to be expressed in brain tissue of all three investigated species. Particularly high expression levels were found in neurons of the red nucleus in human tissue, while cortical neurons, pyramidal and granule cells of the hippocampus and dopamine neurons of substantia nigra showed moderate expression levels. Purkinje cells of cerebellum were positive for class III ADH mRNA in all species investigated, whereas granular layer neurons were positive only in rodents. The choroid plexus was highly positive for class III ADH, while no specific signal for class I or class IV ADH was detected. Our results thus support the notion that the only ADH expressed in adult mouse, rat and human brain is class III ADH.

Alcohol dehydrogenase alleles in Parkinson's disease

Mutations in alcohol dehydrogenase (ADH; EC 1.1.1.1) genes may be of interest in the etiology of Parkinson's disease (PD) because of the important role these enzymes play in retinoid and dopamine metabolism and/or aldehyde detoxification. The location of several alcohol dehydrogenase genes in a cluster on chromosome 4 lends further support to ADH genes being candidates for this disorder, because recently a form of autosomal-dominant parkinsonism has been mapped to this area. We sequenced the promoter and coding regions and part of the introns of the human class IV ADH gene in 10 patients with PD. Seven different polymorphisms were identified. These polymorphisms could be assigned to four alleles (A1-A4). We then determined the frequencies of those four alleles and the wild-type allele in 78 patients with PD and 130 control subjects and found a significant association of the A1 allele with PD (odds ratio = 2.87; 95% confidence interval = 1.35-6.08). In familial cases, the association was strongest (odds ratio = 4.86; 95% confidence interval = 1.89-12.75). Two patients were homozygous for A1 whereas none of the 130 control subjects was found to be homozygous. Our results show an association between a certain ADH4 (formerly known as ADH7 in humans) allele and PD. This suggests a role for genetic variations of ADH4 as risk factors for the development of PD. Our data also show that the observed polymorphisms alone are not sufficient to cause symptoms. Further genetic and/or environmental factors have to be involved.

Molecular basis for differential substrate specificity in class IV alcohol dehydrogenases: a conserved function in retinoid metabolism but not in ethanol oxidation

Mammalian class IV alcohol dehydrogenase enzymes are characteristic of epithelial tissues, exhibit moderate to high K(m) values for ethanol, and are very active in retinol oxidation. The human enzyme shows a K(m) value for ethanol which is 2 orders of magnitude lower than that of rat class IV. The uniquely significant difference in the substrate-binding pocket between the two enzymes appears to be at position 294, Val in the human enzyme and Ala in the rat enzyme. Moreover, a deletion at position 117 (Gly in class I) has been pointed out as probably responsible for class IV specificity toward retinoids. With the aim of establishing the role of these residues, we have studied the kinetics of the recombinant human and rat wild-type enzymes, the human G117ins and V294A mutants, and the rat A294V mutant toward aliphatic alcohols and retinoids. 9-cis-Retinol was the best retinoid substrate for both human and rat class IV, strongly supporting a role of class IV in the generation of 9-cis-retinoic acid. In contrast, 13-cis retinoids were not substrates. The G117ins mutant showed a decreased catalytic efficiency toward retinoids and toward three-carbon and longer primary aliphatic alcohols, a behavior that resembles that of the human class I enzyme, which has Gly(117). The K(m) values for ethanol dramatically changed in the 294 mutants, where the human V294A mutant showed a 280-fold increase, and the rat A294V mutant a 50-fold decrease, compared with those of the respective wild-type enzymes. This demonstrates that the Val/Ala exchange at position 294 is mostly responsible for the kinetic differences with ethanol between the human and rat class IV. In contrast, the kinetics toward retinoids was only slightly affected by the mutations at position 294, compatible with a more conserved function of mammalian class IV alcohol dehydrogenase in retinoid metabolism.

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.

Identification of genes differentially over-expressed in lung squamous cell carcinoma using combination of cDNA subtraction and microarray analysis

In order to develop effective vaccine products against human cancer, we are interested in identifying genes over-expressed in tumor cells. Through a combination of cDNA library subtraction and microarray technology, we identified seventeen genes preferentially expressed in lung squamous cell carcinoma, including four novel genes. To date, expression profiles of these genes were confirmed by Northern and/or real-time analysis, and several genes were also found to be expressed in head and neck squamous tumors. Thus, these combined methods represent a high throughput approach for identifying tumor specific genes. Furthermore, the report of characterization on these genes will allow them to be exploited for their diagnostic, prognostic, and therapeutic potentials including immunotherapy and antibody based anticancer therapy.

Good genes, oxidative stress and condition-dependent sexual signals

The immune and the detoxication systems of animals are characterized by allelic polymorphisms, which underlie individual differences in ability to combat assaults from pathogens and toxic compounds. Previous studies have shown that females may improve offspring survival by selecting mates on the basis of sexual ornaments and signals that honestly reveal health. In many cases the expression of these ornaments appears to be particularly sensitive to oxidative stress. Activated immune and detoxication systems often generate oxidative stress by an extensive production of reactive metabolites and free radicals. Given that tolerance or resistance to toxic compounds and pathogens can be inherited, female choice should promote the evolution of male ornaments that reliably reveal the status of the bearers' level of oxidative stress. Hence, oxidative stress may be one important agent linking the expression of sexual ornaments to genetic variation in fitness-related traits, thus promoting the evolution of female mate choice and male sexual ornamentation, a controversial issue in evolutionary biology ever since Darwin.

Alcohol dehydrogenases in Xenopus development: conserved expression of ADH1 and ADH4 in epithelial retinoid target tissues

Mammalian alcohol dehydrogenases ADH1 (class I ADH) and ADH4 (class IV ADH) function as retinol dehydrogenases contributing to the synthesis of retinoic acid, the active form of vitamin A involved in growth and development. Xenopus laevis ADH1 and ADH4 genes were isolated using polymerase chain reaction primers corresponding to conserved motifs of vertebrate ADHs. The predicted amino acid sequence of Xenopus ADH1 was clearly found to be an ortholog of ADH1 from the related amphibian Rana perezi. Phylogenetic tree analysis of the Xenopus ADH4 sequence suggested this enzyme is likely to be an ADH4 ortholog, and this classification was more confidently made when based also on the unique expression patterns of Xenopus ADH1 and ADH4 in several retinoid-responsive epithelial tissues. Northern blot analysis of Xenopus adult tissues indicated nonoverlapping patterns of ADH expression, with ADH1 mRNA found in small intestine, large intestine, liver, and mesonephros and ADH4 mRNA found in esophagus, stomach, and skin. These nonoverlapping tissue-specific patterns are identical to those previously observed for mouse ADH1 and ADH4, thus providing further evidence that Xenopus ADH1 and ADH4 are orthologs of mouse ADH1 and ADH4, respectively. During Xenopus embryonic development ADH1 mRNA was first detectable by Northern blot analysis at stage 35, whereas ADH4 mRNA was undetectable through stage 47. Whole-mount in situ hybridization indicated that ADH1 expression was first localized in the pronephros during Xenopus embryogenesis, thus conserved with mouse embryonic ADH1 which is first expressed in the mesonephros. ADH4 expression was not detected in Xenopus embryos by whole-mount in situ hybridization but was localized to the gastric mucosa of the adult stomach, a property shared by mouse ADH4. Conserved expression of ADH1 and ADH4 in retinoid-responsive epithelial tissues of amphibians and mammals argue that these enzymes may perform essential retinoid signaling functions during development of the pronephros, mesonephros, liver, and lower digestive tract in the case of ADH1 and in the skin and upper digestive tract in the case of ADH4.

Effect of cellular retinol-binding protein on retinol oxidation by human class IV retinol/alcohol dehydrogenase and inhibition by ethanol

All-trans retinoic acid (atRA) is a powerful morphogen synthesized in a variety of tissues. Oxidation of all-trans retinol to all-trans retinal determines the overall rate of atRA biosynthesis. This reaction is catalyzed by multiple dehydrogenases in vitro. In the cells, most all-trans retinol is bound to cellular retinol binding protein (CRBP). Whether retinoic acid is produced from the free or CRBP-bound retinol in vivo is not known. The current study investigated whether human medium-chain alcohol/retinol dehydrogenases (ADH) can oxidize the CRBP-bound retinol. The results of this study suggest that retinol bound to CRBP cannot be channeled to the active site of ADH. Thus, the contribution of ADH isozymes to retinoic acid biosynthesis will depend on the amount of free retinol in each cell. Physiological levels of ethanol will substantially inhibit the oxidation of free retinol by human ADHs: class I, alpha alpha and beta 2 beta 2; class II, pi pi; and class IV, sigma sigma.

Regulation of human alcohol dehydrogenase gene ADH7: importance of an AP-1 site

The structure and function of the human alcohol dehydrogenase 7 (ADH7) promoter were analyzed. A promoter fragment extending to bp -232 functioned well in H4IIE-C3, CV-1, and HeLa cells, whereas the region extending further upstream to bp -799 had no significant effect on activity. We identified cis-acting elements in the proximal 232 bp and examined their effect on promoter activity. Mutation of site A, where c-Jun bound, caused a drastic decrease in the promoter activity in H4IIE-C3 and CV-1 cells, suggesting that AP-1 plays an important role in the regulation of ADH7. Mutation of site B also caused a large drop in promoter activity in both cell lines; C/EBPalpha can bind to this site, but because the site affects activity approximately equally in CV-1 cells that lack C/EBPalpha and in H4IIE-C3 cells that contain low levels, other proteins are likely to play the major roles in vivo. Mutation of site C, where C/EBP bound and c-Jun bound weakly, had different effects in the two cell lines: in H4IIE-C3 cells, the site C mutation did not significantly increase promoter activity, whereas in CV-1 cells, which lack C/EBPalpha, it led to a doubling of activity. Surprisingly, cotransfection of the wild-type promoter with C/EBPa or C/EBPbeta led to a decrease in promoter activity, which might in part explain the lack of activity of ADH7 in adult liver.

Gene structure and promoter for Adh3 encoding mouse class IV alcohol dehydrogenase (retinol dehydrogenase)

Class IV alcohol dehydrogenase (ADH) has been shown to function in vitro as a retinol dehydrogenase catalyzing the synthesis of retinoic acid, a pleiotropic gene regulator. To enable genetic studies on the function of this enzyme and regulation of its gene, we have screened a genomic library and isolated the mouse class IV ADH gene (Adh3). The complete mouse class IV ADH coding region was found in nine exons spanning a 14-kb region. Primer extension analysis was used to map the transcription initiation site to a position lying 30 bp upstream of the ATG translation start codon. Nucleotide sequence analysis of the promoter region indicated an absence of both TATA-box and GC-box sequences; this distinguishes it from the promoters for class I, II, and III ADH genes. Sequence comparison of the mouse and human class IV ADH promoters indicated that they share a conserved region located 125-145 bp upstream of the coding region containing adjacent sequences matching the consensus binding sites for transcription factors AP-1 and C/EBP.

Failure to find exon 7 polymorphism of the ADH7 gene in Chinese, Japanese, African-Americans, and Caucasians

Class IV alcohol dehydrogenase (sigma-ADH) activity has been found in high levels in the stomach and esophagus, but not in liver. Gastric ADH activity has been reported to influence blood alcohol levels after oral ethanol ingestion, suggesting that sigma-ADH activity plays a role in first-pass metabolism. It has also been reported that women have lower sigma-ADH activity than men and that Asians have lower sigma-ADH activity than Caucasians and African-Americans. A genetic basis for these gender and ethnic differences in sigma-ADH activity has been postulated. A recent study in a Japanese subject found a point mutation in the codon for amino acid 287 of the ADH7 gene (which encodes sigma-ADH), changing the amino acid from glycine to valine. A polymerase chain reaction-sequencing assay was established to determine the frequency of this polymorphism in the Asian, Caucasian, and African-American populations. The polymorphism was not present in the 21 Asians, 15 Caucasians, and 3 African-Americans we genotyped, suggesting that if this polymorphism exists, its frequency is low in these ethnic groups. It is therefore unlikely to be responsible for the absence of sigma-ADH activity in gastric specimens from Asians.

Cloning of the mouse class IV alcohol dehydrogenase (retinol dehydrogenase) cDNA and tissue-specific expression patterns of the murine ADH gene family

Humans possess five classes of alcohol dehydrogenase (ADH), including forms able to oxidize ethanol or formaldehyde as part of a defense mechanism, as well as forms acting as retinol dehydrogenases in the synthesis of the regulatory ligand retinoic acid. However, the mouse has previously been shown to possess only three forms of ADH. Hybridization analysis of mouse genomic DNA using cDNA probes specific for each of the five classes of human ADH has now indicated that mouse DNA cross-hybridizes to only classes I, III, and IV. With human class II or class V ADH cDNA probes, hybridization to mouse genomic DNA was very weak or undetectable, suggesting either a lack of these genes in the mouse or a high degree of mutational divergence relative to the human genes. cDNAs for murine ADH classes I and III have previously been cloned, and we now report the cloning of a full-length mouse class IV ADH cDNA. In Northern blot analyses, mouse class IV ADH mRNA was abundant in the stomach, eye, skin, and ovary, thus correlating with the expression pattern for the mouse Adh-3 gene previously determined by enzyme analysis. In situ hybridization studies on mouse stomach indicated that class IV ADH transcripts were abundant in the mucosal epithelium but absent from the muscular layer. Comparison of the expression patterns for all three mouse ADH genes indicated that class III was expressed ubiquitously, whereas classes I and IV were differentially expressed in an overlapping set of tissues that all contain a large component of epithelial cells. This expression pattern is consistent with the ability of classes I and IV to oxidize retinol for the synthesis of retinoic acid known to regulate epithelial cell differentiation. The results presented here indicate that the mouse has a simpler ADH gene family than the human but has conserved class IV ADH previously shown to be a very active retinol dehydrogenase in humans.