Multiple mRNAs for human alcohol dehydrogenase (ADH): developmental and tissue specific differences

The evolution and population genetics of the ALDH2 locus: random genetic drift, selection, and low levels of recombination

The catalytic deficiency of human aldehyde dehydrogenase 2 (ALDH2) is caused by a nucleotide substitution (G1510A; Glu487Lys) in exon 12 of the ALDH2 locus. This SNP, and four non-coding SNPs, including one in the promoter, span 40 kb of ALDH2; these and one downstream STRP have been tested in 37 worldwide populations. Only four major SNP-defined haplotypes account for almost all chromosomes in all populations. A fifth haplotype harbours the functional variant and is only found in East Asians. Though the SNPs showed virtually no historic recombination, LD values are quite variable because of varying haplotype frequencies, demonstrating that LD is a statistical abstraction and not a fundamental aspect of the genome, and is not a function solely of recombination. Among populations, different sets of tagging SNPs, sometimes not overlapping, can be required to identify the common haplotypes. Thus, solely because haplotype frequencies vary, there is no common minimum set of tagging SNPs globally applicable. The Fst values of the promoter region SNP and the functional SNP were about two S.D. above the mean for a reference distribution of 117 autosomal biallelic markers. These high Fst values may indicate selection has operated at these or very tightly linked sites.

The role of vitamin A in mammalian reproduction and embryonic development

Since the late 1980s, there has been an explosion of information on the molecular mechanisms and functions of vitamin A. This review focuses on the essential role of vitamin A in female reproduction and embryonic development and the metabolism of vitamin A (retinol) that results in these functions. Evidence strongly supports that in situ-generated all-trans retinoic acid (atRA) is the functional form of vitamin A in female reproduction and embryonic development. This is supported by the ability to reverse most reproductive and developmental blocks found in vitamin A deficiency with atRA, the block in embryonic development that occurs in retinaldehyde dehydrogenase type 2 null mutant mice, and the essential roles of the retinoic acid receptors, at least in embryogenesis. Early studies of embryos from marginally vitamin A-deficient (VAD) pregnant rats revealed a collection of defects called the vitamin A-deficiency syndrome. The manipulation of all-trans retinoic acid (atRA) levels in the diet of VAD female rats undergoing a reproduction cycle has proved to be an important new tool in deciphering the points of atRA function in early embryos and has provided a means to generate large numbers of embryos at later stages of development with the vitamin A-deficiency syndrome. The essentiality of the retinoid receptors in mediating the activity of atRA is exemplified by the many compound null mutant embryos that now recapitulate both the original vitamin A-deficiency syndrome and exhibit a host of new defects, many of which can also be observed in the VAD-atRA-supported rat embryo model and in retinaldehyde dehydrogenase type 2 (RALDH2) mutant mice. A major task for the future is to elucidate the atRA-dependent pathways that are normally operational in vitamin A-sufficient animals and that are perturbed in deficiency, thus leading to the characteristic VAD phenotypes described above.

Expression of genes for alcohol and aldehyde metabolizing enzymes in mouse oocytes and preimplantation embryos

Alcohols and aldehydes are metabolized primarily by alcohol (ADH) and aldehyde (ALDH) dehydrogenase isozymes. Although significant progress has been made towards understanding the involvement of these isozymes in the oxidation of alcohol and aldehydes in the body, it is not known how these compounds are handled during fertilization and preimplantation embryogenesis. In this study, reverse transcription and the polymerase chain reaction (RT-PCR) was used to determine which ADH and ALDH isozymes are expressed at the oocyte, zygote, morula, and blastocyst stages of preimplantation development in the mouse. Transcripts of beta-actin and vimentin, assayed as controls, were detected at all stages, as well as Class III ADH (Adh-2) and Class 3 ALDH (Ahd-4), involved in the detoxification of formaldehyde and aromatic aldehydes, respectively. In contrast, transcripts for the major ethanol oxidizing isozyme, Class I ADH (Adh-1) was not detected during preimplantation development. Cytosolic retinol dehydrogenase (Adh-3) transcripts were marginally detected in oocytes and zygotes. The mRNA for cytosolic retinal dehydrogenase (Ahd-2), microsomal short-chain retinol dehydrogenases (RoDH Type I), and the mitochondrial low-Km acetaldehyde dehydrogenase (Ahd-5) only appeared as maternal transcripts. Microsomal ALDH (Ahd-3), which is induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), was not expressed until the blastocyst stage. ADH and ALDH enzyme systems may guard mouse preimplantation embryos against the toxic effects of industrial pollutants, such as formaldehyde and TCDD, as well as peroxidatic aldehydes generated during lipid peroxidation. The absence of enzymes to convert ethanol to acetaldehyde, coupled with oocyte expression of the acetaldehyde-degrading enzyme, Ahd-5, may be protective for the early embryo.

Molecular analysis of genetic differences among inbred mouse strains controlling tissue expression pattern of alcohol dehydrogenase 4

The ADH gene family in vertebrates is composed of at least seven distinct classes based upon sequence comparisons and enzyme properties. The Adh4 gene product may play an important role in differentiation and development because of its capacity to metabolize retinol to retinoic acid. Allelic gene differences exist among inbred mouse strains which control structure and tissue-specific regulation of Adh4. C57BL/6 mice are unique and have no detectable ADH4 enzyme activity in epididymis and low levels in seminal vesicle, ovary and uterus compared to other strains. C57BL/6 mice express Adh4 in stomach at levels similar to other strains. The goal of this research was to investigate this genetic variation at the molecular level. Northern analysis revealed that the content of ADH4 mRNA in tissues correlate with the enzyme expression pattern. Interestingly, C57BL/6 mice express an ADH4 mRNA in stomach which is smaller than expressed in C3H and other mice. An analysis of the 5'- and 3'-ends of the mRNA using RACE analysis determined that the ADH4 mRNA in C57BL/6 mice is truncated in the 3'-untranslated region. Sequence analysis of RACE products showed that the truncation is due to a single nucleotide mutation which produces an early polyadenylation signal. Additional RACE and Northern analysis revealed that at least five different polyadenylation sites are used in the Adh4 gene. Using 3'-end polymorphisms found between C57BL/6 and C3H strains and RT-PCR, it was shown that the lack of expression in epididymis in C57BL/6 mice is cis-acting in F(1) hybrid animals. The DNA sequence of the proximal promoter (-600/+42 nt) was determined in several mouse strains differing in tissue-specific expression patterns and did not reveal any nucleotide substitutions correlating with expression pattern suggesting further upstream or downstream sequences may be involved.

Families of retinoid dehydrogenases regulating vitamin A function: production of visual pigment and retinoic acid

Vitamin A (retinol) and provitamin A (beta-carotene) are metabolized to specific retinoid derivatives which function in either vision or growth and development. The metabolite 11-cis-retinal functions in light absorption for vision in chordate and nonchordate animals, whereas all-trans-retinoic acid and 9-cis-retinoic acid function as ligands for nuclear retinoic acid receptors that regulate gene expression only in chordate animals. Investigation of retinoid metabolic pathways has resulted in the identification of numerous retinoid dehydrogenases that potentially contribute to metabolism of various retinoid isomers to produce active forms. These enzymes fall into three major families. Dehydrogenases catalyzing the reversible oxidation/reduction of retinol and retinal are members of either the alcohol dehydrogenase (ADH) or short-chain dehydrogenase/reductase (SDR) enzyme families, whereas dehydrogenases catalyzing the oxidation of retinal to retinoic acid are members of the aldehyde dehydrogenase (ALDH) family. Compilation of the known retinoid dehydrogenases indicates the existence of 17 nonorthologous forms: five ADHs, eight SDRs, and four ALDHs, eight of which are conserved in both mouse and human. Genetic studies indicate in vivo roles for two ADHs (ADH1 and ADH4), one SDR (RDH5), and two ALDHs (ALDH1 and RALDH2) all of which are conserved between humans and rodents. For several SDRs (RoDH1, RoDH4, CRAD1, and CRAD2) androgens rather than retinoids are the predominant substrates suggesting a function in androgen metabolism as well as 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.

Alcohol dehydrogenase in human tissues: localisation of transcripts coding for five classes of the enzyme

Tissue distribution of the five identified classes of human alcohol dehydrogenase was studied by assessment of mRNA levels in 23 adult and four fetal tissues. Alcohol dehydrogenase of class I was found in most tissues, brain and placenta excluded, but expression levels among tissues differed widely. The distribution pattern of class III transcripts was consistent with those of housekeeping enzymes while, in contrast, class IV transcripts were found only in stomach. Transcripts of multiple length were detected for most classes and were due to different gene products arising through the use of different poly-A signals or transcription from different gene loci. Both class II and class V showed a pattern of liver-enriched expression. However, low mRNA levels were detected also in stomach, pancreas and small intestine for class II, and in fetal kidney and small intestine for class V. Significantly higher levels of class V transcripts were present in fetal liver when compared with levels in adult liver, which suggests that human class V is a predominantly fetal alcohol dehydrogenase.

The class I alcohol dehydrogenase gene is glucocorticoid-responsive in the rat hepatoma microcell hybrid cell line, 11-3

Expression of the class I alcohol dehydrogenase (ADH) gene in the rat hepatoma microcell hybrid cell line, 11-3, was examined. The steady-state level of ADH mRNA in 11-3 was approximately 2-fold higher than that or rat liver and Fao, the parental cell line of 11-3. Removal of steroid hormones by activated charcoal from the serum in which 11-3 cells were maintained resulted in a significant decrease in the level of ADH transcript. Dexamethasone at a concentration of 1 muM increased the ADH mRNA content in 11-3 in a time-dependent fashion, up to 48 hr after its addition to cells that had first been deprived of steroid hormones. In addition, levels of ADH transcript in cells treated with dexamethasone increased in a dose-dependent manner, and the concentration of dexamethasone required to achieve half-maximal activation was 5 nM. By using the techniques of reverse transcription and polymerase chain reaction, and by taking advantage of a restriction polymorphism present between the rat and mouse ADH cDNA, we found that 11-3 contained both the rat and mouse class I ADH transcripts, although the rat sequence accounted for the great majority. Moreover, levels of both rat and mouse class I ADH transcripts increased in a similarly time-dependent manner in cells treated with dexamethasone. These results indicate that expression of class I ADH gene in 11-3 is high and is regulated by glucocorticoids, making the cell line an excellent model for the in vitro study of ADH expression.

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

Human alcohol dehydrogenase (ADH) consists of a family of five evolutionarily related classes of enzymes that collectively function in the metabolism of a wide variety of alcohols including ethanol and retinol. Class IV ADH has been found to be the most active as a retinol dehydrogenase, thus it may participate in retinoic acid synthesis. The gene encoding class IV ADH (ADH7) has now been cloned and subjected to molecular examination. Southern blot analysis indicated that class IV ADH is encoded by a single unique gene and has no related pseudogenes. The class IV ADH gene is divided into nine exons, consistent with the highly conserved intron/exon structure of other mammalian ADH genes. The predicted amino acid sequence of the exon coding regions indicates that a protein of 373 amino acids, excluding the amino-terminal methionine, would be translated, sharing greater sequence identity with class I ADH (69%) than with classes II, III or V (59-61%). Expression of class IV ADH mRNA was detected in human stomach but not liver. This correlates with previous protein studies, which have indicated that class IV ADH is the major stomach ADH but unlike other ADHs is absent from liver. Primer extension studies using human stomach RNA were performed to identify the transcription initiation site lying 100 base pairs upstream of the ATG translation start codon. Nucleotide sequence analysis of the promoter region indicated the absence of a TATA box sequence often located about 25 base pairs upstream of the start site as well as the absence of GC boxes, which are quite often seen in promoters lacking a TATA box. The class IV ADH promoter thus differs from the other ADH promoters, which contain either a TATA box (classes I and II) or GC-boxes (class III), suggesting a fundamentally different form of transcriptional regulation.

Distribution of alcohol and sorbitol dehydrogenases. Assessment of mRNA species in mammalian tissues

The tissue distribution of mRNA of alcohol dehydrogenases of classes I, II and III, and sorbitol dehydrogenase, was studied. mRNA from 19 different rat tissues was purified and analyzed by Northern blots, utilizing cDNA probes specific for the four dehydrogenases. Class-I alcohol-dehydrogenase mRNA was shown to be of widespread occurrence, detectable in all tissues including brain, but with pronounced differences in amounts. Hybridization revealed the pattern of occurrence of class-II alcohol-dehydrogenase mRNA to be unique, with transcripts only in the liver, duodenum, kidney, stomach, spleen and testis. Abundant levels of class-III alcohol-dehydrogenase (glutathione-dependent formaldehyde dehydrogenase) mRNA were present in all tissues analyzed, reflecting the general need for scavenging of formaldehyde in physiological cytoprotection. Sorbitol dehydrogenase mRNA was detected in all tissues except small intestine, in agreement with sorbitol resorbtion by passive diffusion in this tissue. In addition, evidence for a sex-specific expression, in the liver, of class-II alcohol dehydrogenase was obtained.

Isozyme developments in mammalian class-I alcohol dehydrogenase. cDNA cloning, functional correlations, and lack of evidence for genetic isozymes in rabbit

Isozyme patterns differ widely among the classical type (class I) of mammalian alcohol dehydrogenases. For the rabbit enzyme, the possibility of isozymes has been reported but structural evidence is lacking. This system was now studied at both the mRNA/cDNA and protein levels. Ten cDNA clones, coding for class-I alcohol dehydrogenase, were isolated from a rabbit liver cDNA library using a human DNA fragment as probe. The cDNA spanned 1296 bp, including the entire coding region. All clones coded for the same polypeptide and Northern blots identified a single mRNA corresponding to about 1.5 kb. Comparison of two protein forms (CC and BC) by HPLC peptide fingerprinting and structural analysis revealed peptide segments identical in amino acid sequence. Consequently, direct protein analyses and Northern blots show the presence of only one primary translation product. The data suggest that lagomorphic alcohol dehydrogenase, like the rodent enzyme, is not as isozyme rich as it may appear superficially, and that secondary modifications contribute substantially to mammalian alcohol dehydrogenase multiplicity. The active center of the rabbit enzyme suggests similarities to the horse S, human gamma, and rat enzyme structures, compatible with a steroid dehydrogenase activity shown experimentally. Typical class-I properties were established by direct analysis and confirmed by structural properties (Km for cyclohexanol 0.8-1.1 mM, for ethanol 1.6-1.9 mM). The isozyme versus species differences mark the variability of class-I alcohol dehydrogenase versus class III and suggest a parallelism between rapid mutational differences and frequent duplicatory events.

The first 22 base pairs of the proximal promoter of the rat class I alcohol dehydrogenase gene is bipartite and interacts with multiple DNA-binding proteins

The rat class I alcohol dehydrogenase (ADH) gene is primarily expressed in the liver. We previously showed that the liver-enriched transcription factor, the CCAAT/enhancer binding protein (C/EBP), binds to the proximal promoter of the rat class I ADH gene between positions -11 and -22 relative to the start site of transcription. We now demonstrate that another transcription factor, the liver activator protein (LAP), also interacts with the same region of the promoter based on the following observations: (1) LAP synthesized by in vitro transcription and translation of cloned cDNA sequence forms complexes with an oligonucleotide containing the C/EBP-binding sequence within the ADH promoter as determined by the electrophoretic mobility shift assay (EMSA), (2) purified LAP interacts with the proximal ADH promoter when analyzed by the DNase I protection assay, and (3) an ADH promoter-reporter gene construct containing the C/EBP-binding site is transactivated by an eukaryotic expression vector containing the LAP sequence. EMSA of an oligonucleotide containing the first 22 base pairs (between positions -1 and -22) of the ADH promoter with rat liver nuclear extracts (RLNE) resulted in the formation of two major complexes. Complex 1 was competed away by a heterologous oligonucleotide containing a C/EBP-binding site within the promoter of the adipocyte 422 (aP2) gene, while complex 2 was not. Additional competition experiments with the ADH or 422 (aP2) oligonucleotide using either RLNE or extracts from 3T3-L1 adipocytes demonstrated that complex 1 contains either C/EBP or LAP, while complex 2 contains a DNA-binding protein that binds to a novel sequence 5'-TGGCCCAGTT-3' between positions -1 and -10 of the ADH promoter. Ultraviolet cross-linking between RLNE and a labeled oligonucleotide containing the above sequence indicates that this protein, designated EDBP (for enhancer-site downstream binding protein), has an estimated molecular weight of 47 kDa, which is larger than that reported for either C/EBP (42 kDa) or LAP (36 kDa).

Expression of CYP2E1 during human fetal development: methylation of the CYP2E1 gene in human fetal and adult liver samples

The expression and regulation of cytochrome P450IIE1 (CYP2E1) in adult and fetal human liver has been investigated. Three mRNA transcripts of 1.9, 2.7 and 3.8 kb were detected in all adult liver samples after hybridization with a full length cDNA to CYP2E1 whereas no expression was detected in 12 fetal liver samples studied. Similarly, expression of CYP2E1 was not detected in 11 placental samples (10-17 weeks gestational age) or in two full-term placental samples. CYP2E1 expression was not detected in fetal liver, kidney, lung, placenta (18 weeks gestational age) or liver (6 weeks gestational age) obtained at termination of pregnancy where maternal alcohol abuse had been established. Southern blot analysis of the cytosine methylation status of the CYP2E1 gene revealed substantial methylation of the 3' region of the gene in both adult and fetal human liver samples. No differences were observed in the methylation pattern of fetal liver samples between the gestational ages 12 and 17 weeks. Two small DNA fragments detected by the 5' end of the CYP2E1 cDNA were cleaved by the restriction enzyme HpaII in adult liver DNA but not in the fetal liver DNA samples. Methylation of specific 5' residues in the CYP2E1 gene may be responsible for the lack of transcription of the CYP2E1 gene in fetal liver.

Estrogen induction of alcohol dehydrogenase in the uropygial gland of mallard ducks

Treatment of mallard ducks with estradiol, or a combination of estradiol and thyroxine, has been shown to result in the proliferation of peroxisomes and production of diesters of 3-hydroxy fatty acids, the female pheromones, in the uropygial gland of male and female mallard ducks. Such a treatment results in the induction of a unique set of proteins. A cDNA library enriched in hormone-induced transcripts was subjected to differential screening. The nucleotide sequence of one of the two unique cDNA clones, DGH1, had high similarity to the Human class I alcohol dehydrogenase (ADH) gamma subunit and represented the carboxy-terminus of the protein from amino acid 190-374. SDS/PAGE and Western blot analysis of the proteins indicated that the level of a 38-kDa protein that cross-reacted with antibodies prepared against the chicken ADH was increased 5-7-fold by hormone treatment. Assays for ADH activity in the uropygial gland extracts of male mallards showed a 5-7-fold induction of the enzyme by hormone treatment. The 1.9-kb ADH mRNA levels were increased 12-14-fold under these conditions. Of all the tissues tested, the uropygial gland had the highest levels of ADH mRNA. Induction of ADH by estradiol treatment occurred only in this tissue. Elevated levels of ADH were also observed in the glands of male mallards in eclipse, the post-nuptial condition when the hormonal balance is shifted to higher estrogen levels, suggesting that this enzyme is regulated by estrogens in this period. Estradiol treatment caused an 80% decrease in the NAD+/NADH ratio in the uropygial gland and a twofold increase in the fatty alcohol oxidation rate catalyzed by the gland extract. These observations could help explain how increased levels of ADH could contribute to the production of the diesters.

A hypothetical mechanism for fetal alcohol syndrome involving ethanol inhibition of retinoic acid synthesis at the alcohol dehydrogenase step

Ethanol acts as a teratogen causing brain, craniofacial, and limb abnormalities in those suffering from fetal alcohol syndrome. Normal embryonic development of the vertebrate nervous system and limbs has recently been shown to be governed by retinoic acid, the active form of vitamin A. Retinol dehydrogenase is an enzyme needed to convert vitamin A (retinol) to retinoic acid, a molecule that specifies embryonic pattern formation by controlling gene expression. Ethanol acts as a competitive inhibitor of the retinol dehydrogenase activity attributed to mammalian alcohol dehydrogenase (ADH), an enzyme that uses both retinol and ethanol as substrates. An hypothesis is presented in which many of the abnormalities observed in fetal alcohol syndrome may be caused by high levels of ethanol acting as a competitive inhibitor of ADH-catalyzed retinol oxidation in the embryo or fetus. This would presumably result in a reduction of retinoic acid synthesis in embryonic tissues such as the nervous system and limbs that require critical levels of this molecule to specify spatial patterns.

Retinoic acid response element in the human alcohol dehydrogenase gene ADH3: implications for regulation of retinoic acid synthesis

Retinoic acid regulation of one member of the human class I alcohol dehydrogenase (ADH) gene family was demonstrated, suggesting that the retinol dehydrogenase function of ADH may play a regulatory role in the biosynthetic pathway for retinoic acid. Promoter activity of human ADH3, but not ADH1 or ADH2, was shown to be activated by retinoic acid in transient transfection assays of Hep3B human hepatoma cells. Deletion mapping experiments identified a region in the ADH3 promoter located between -328 and -272 bp which confers retinoic acid activation. This region was also demonstrated to confer retinoic acid responsiveness on the ADH1 and ADH2 genes in heterologous promoter fusions. Within a 34-bp stretch, the ADH3 retinoic acid response element (RARE) contains two TGACC motifs and one TGAAC motif, both of which exist in RAREs controlling other genes. A block mutation of the TGACC sequence located at -289 to -285 bp eliminated the retinoic acid response. As assayed by gel shift DNA binding studies, the RARE region (-328 to -272 bp) of ADH3 bound the human retinoic acid receptor beta (RAR beta) and was competed for by DNA containing a RARE present in the gene encoding RAR beta. Since ADH catalyzes the conversion of retinol to retinal, which can be further converted to retinoic acid by aldehyde dehydrogenase, these results suggest that retinoic acid activation of ADH3 constitutes a positive feedback loop regulating retinoic acid synthesis.

Retinoic acid response element in the human alcohol dehydrogenase gene ADH3: implications for regulation of retinoic acid synthesis

Retinoic acid regulation of one member of the human class I alcohol dehydrogenase (ADH) gene family was demonstrated, suggesting that the retinol dehydrogenase function of ADH may play a regulatory role in the biosynthetic pathway for retinoic acid. Promoter activity of human ADH3, but not ADH1 or ADH2, was shown to be activated by retinoic acid in transient transfection assays of Hep3B human hepatoma cells. Deletion mapping experiments identified a region in the ADH3 promoter located between -328 and -272 bp which confers retinoic acid activation. This region was also demonstrated to confer retinoic acid responsiveness on the ADH1 and ADH2 genes in heterologous promoter fusions. Within a 34-bp stretch, the ADH3 retinoic acid response element (RARE) contains two TGACC motifs and one TGAAC motif, both of which exist in RAREs controlling other genes. A block mutation of the TGACC sequence located at -289 to -285 bp eliminated the retinoic acid response. As assayed by gel shift DNA binding studies, the RARE region (-328 to -272 bp) of ADH3 bound the human retinoic acid receptor beta (RAR beta) and was competed for by DNA containing a RARE present in the gene encoding RAR beta. Since ADH catalyzes the conversion of retinol to retinal, which can be further converted to retinoic acid by aldehyde dehydrogenase, these results suggest that retinoic acid activation of ADH3 constitutes a positive feedback loop regulating retinoic acid synthesis.

Multiplication of the class I alcohol dehydrogenase locus in mammalian evolution

Chromosomal DNA samples derived from various primates and other mammals (horse, sheep, rabbit, and mouse) were digested with restriction endonuclease and hybridized with a probe of the sixth exon of the human ADH gene, which is highly conserved in the class I alcohol dehydrogenase of these mammalian species. The copy number of the class I ADH gene in each species was estimated from the number of hybridized bands. Primate DNA samples showed three distinct bands in the blots of PstI digest and DraI digest. Moreover, most of the bands from primate DNA showed a similarity in size so as to allow us to assign the ADH1, ADH2, and ADH3 homologues in each species. In contrast, mouse has only one gene, and rabbit, sheep, and horse seem to have only two genes, for the class I ADH, which showed divergent hybridization bands. These results are consistent with the view that the human class I ADH gene cluster has been generated through gene multiplication events which occurred before the Catarrhini branch point in the course of primate evolution.

trans activation of human alcohol dehydrogenase gene expression in hepatoma cells by C/EBP molecules bound in a novel arrangement just 5' and 3' to the TATA box

A promoter sequence between nucleotide -51 and nucleotide -10 in the human alcohol dehydrogenase gene ADH2 has been shown to bind the transcription factor CCAAT/enhancer-binding protein (C/EBP). A series of 5'-end deletions of the ADH2 promoter was cotransfected with a C/EBP expression plasmid in a human hepatoma cell line, and trans activation by C/EBP was seen when at least 171 base pairs of 5'-flanking DNA was present. Mutations in the ADH2 promoter indicate that the mechanism of C/EBP trans activation involves two binding sites, one located just upstream of the TATA box and one located in an unusual location between the TATA box and the transcription start point.

trans activation of human alcohol dehydrogenase gene expression in hepatoma cells by C/EBP molecules bound in a novel arrangement just 5' and 3' to the TATA box

A promoter sequence between nucleotide -51 and nucleotide -10 in the human alcohol dehydrogenase gene ADH2 has been shown to bind the transcription factor CCAAT/enhancer-binding protein (C/EBP). A series of 5'-end deletions of the ADH2 promoter was cotransfected with a C/EBP expression plasmid in a human hepatoma cell line, and trans activation by C/EBP was seen when at least 171 base pairs of 5'-flanking DNA was present. Mutations in the ADH2 promoter indicate that the mechanism of C/EBP trans activation involves two binding sites, one located just upstream of the TATA box and one located in an unusual location between the TATA box and the transcription start point.

Developmental changes of aldehyde dehydrogenase isozymes in human livers: mitochondrial ALDH2 isozyme is expressed in fetal livers

Previous reports suggested that the major cytosolic aldehyde dehydrogenase (ALDH1) was present in fetal and infant livers, but the major mitochondrial isozyme (ALDH2) was absent or severely diminished. Re-examination by means of starch gel electrophoresis followed by enzyme activity staining, and by means of dot blot immuno-hybridization of liver samples with known genotypes of the ALDH2 locus, indicated that both ALDH1 and ALDH2 genes are expressed in fetal and infant livers. In addition, ALDH4 isozyme was also observed. The results imply that a fetus with the 'usual' homozygous ALDH1(2)/ALDH1(2) genotype, but not one with the atypical ALDH1(2)/ALDH2(2) or ALDH2(2)/ALDH2(2), is capable of detoxifying acetaldehyde transferred from the mother.

Promoters for the human alcohol dehydrogenase genes ADH1, ADH2, and ADH3: interaction of CCAAT/enhancer-binding protein with elements flanking the ADH2 TATA box

The human ADH1, ADH2, and ADH3 genes are closely related members of a gene family which are differentially expressed during liver development. To begin examining the mechanism of this tissue-specific and stage-specific expression, the 5'-flanking nucleotide (nt) sequences of the three genes were determined and the transcription start point (tsp) were identified. Sequences of all three genes indicated a high degree of homology (greater than 80% nt sequence identity) from the AUG translation start codon to about nt -780 relative to the tsp. Transient transfection assays of a set of plasmids containing various lengths of ADH 5'-flanking DNA fused to cat were performed in the HepG2 and Hep3B human hepatoma cell lines. The results indicated that the ADH2 promoter-proximal region was transcriptionally active in the absence of upstream sequences. To identify potential cis-acting elements in the ADH2 promoter-proximal region, a DNase I footprinting assay using a rat liver nuclear extract was used. Protection occurred in several locations including one, between nt -51 and -10, which shares homology with known binding sites for a previously identified rat-liver transcription factor called CCAAT/enhancer binding protein (C/EBP). Purified C/EBP was shown by footprint analysis to bind at two distinct sites in the ADH2 promoter located at nt -51 to -31 and -21 to -10. The TATA-box promoter element at nt -30 to -22 was not protected by C/EBP, but was partially protected by a factor in the rat liver nuclear extract. Thus, it is possible that the flanking C/EBP molecules may create a novel binding pocket for TFIID, the TATA-binding general transcription factor for RNA polymerase II. Alternatively, the C/EBP molecules may block access to the TATA box, and stimulate transcription of ADH2 by interacting with some component(s) other than TFIID.

The human class I alcohol dehydrogenase gene cluster: three genes are tandemly organized in an 80-kb-long segment of the genome

The class I alcohol dehydrogenases (ADH; EC 1.1.1.1) play a key role in hepatic alcohol catabolism. Three human class I ADH genes, ADH1, ADH2, and ADH3, which encode the alpha, beta, and gamma subunits respectively, have been isolated and mapped on chromosome 4q21-q23. Genomic cloning using a cosmid vector allowed us to obtain an 88-kb-long genomic segment, which was found to include an entire 80 kb of the class I ADH gene cluster. All three genes lie in the same transcriptional orientation and the order of genes is 5'-ADH3-ADH2-ADH1-3'. It may be of some significance that the order of transcriptional activation in the hepatic development, alpha----beta----gamma, is opposite to the order of gene arrangement. Several members of the AluI family and the KpnI (L1) family of interspersed repetitive sequences were mapped in this region. The divergence of insertional sites suggested that gene multiplication of the class I ADH genes had taken place in the earlier stages of human (or primate) evolution.

Structure of cDNA of cytosolic aspartate aminotransferase of chicken and its expression in E. coli

The structure of the mRNA of chicken cytosolic aspartate aminotransferase has been determined by analysis of cDNA and genomic clones. Two transcripts of different length were found that appear to arise from the alternate use of 2 polyadenylation signals in the 3' untranslated region. The expression product of the full-length construct in E. coli proved to be catalytically active and possessed the expected molecular weight.

Organization and expression of the COX6 genetic locus in Saccharomyces cerevisiae: multiple mRNAs with different 3' termini are transcribed from COX6 and regulated differentially

COX6 and its surrounding genetic locus have been characterized for the yeast Saccharomyces cerevisiae. Flanking genes are found closely spaced upstream and downstream of COX6. The upstream gene and COX6 are transcribed from opposite strands and are separated by no more than 300 bp. COX6 is transcribed into three different size classes of mRNA (1000b, 830b, and 700b) differing in length in their 3' untranslated regions. All three classes of mRNAs are found on polysomes and, hence, are most likely translated. The different COX6 mRNAs vary in abundance during growth in rich media and are affected differentially as cells are shifted into media containing high or low glucose concentrations. The largest mRNA is much more susceptible to glucose repression/derepression than are the two smaller mRNAs, whereas the smallest RNA is preferentially accumulated during growth in rich media. These findings demonstrate that COX6 mRNAs with different 3'-termini are either synthesized differentially or differ in stability and suggest the existence of a complex system regulating COX6 expression.

Fat feeding stimulates only one of the two mRNAs encoding rat intestinal membranous and secreted alkaline phosphatase

We have identified two mRNAs in rat intestinal mucosa by Northern blot analysis, using cloned cDNAs encoding human placental alkaline phosphatase (PLAP). Probes from both the NH2- and COOH-terminal ends of the human PLAP coding region identified, in rat intestine (especially duodenum), an mRNA of nearly identical size (3 kb) to that found in human placenta. A smaller mRNA (2.7 kb), detected only with the COOH-terminal probe, was more prevalent in jejunum. Following feeding of triacylglycerols, the prevalence of the 2.7 kb mRNA increased over 2-fold. The tissue distribution and response of the 2.7 kb mRNA to fat feeding corresponds exactly with the known behavior of the secreted alkaline phosphatase.

mRNA for the three human alcohol dehydrogenase subunits: size heterogeneity and developmental changes

Human alcohol dehydrogenase consists of three types of subunits (alpha, beta, and gamma) which are governed by three separate loci. mRNA components for the three subunits were examined by Northern blot hybridization, using a common cDNA probe and specific oligonucleotide probes. A marked size heterogeneity of beta mRNA, ranging from 1.6 kb to 5.2 kb (of which the 2.4-kb and 3.5-kb were major), was observed in the adult liver. The mRNA for the gamma subunit was homogeneous (about 1.6 kb), and that for the alpha subunit contained a major 1.6-kb and a minor 4.3-kb component. The amount of mRNA was much lower (approximately 10% of adult) and the mRNA was less heterogeneous in the infant liver; i.e., an alpha mRNA (1.6 kb) and two beta mRNAs (a major 1.6 kb and a minor 3.5 kb), and no detectable gamma mRNA. The short beta mRNA, with 1.6 kb, could not be hybridized with a non-coding cDNA fragment that originated from the 3'-end of the 2.6 kb beta cDNA. The observed multiple ADH mRNAs, with a common coding region and different 3'-untranslated regions, are generated by utilization of multiple polyadenylation signals. The selection of polyadenylation signals and the rate of transcription of the three ADH loci are developmentally regulated. The 4.3-kb-long mRNA, which was hybridized with both a- and beta-specific probes, could be related to the previously cloned "fused beta-alpha" cDNA.