Characterization of the 5'-flanking sequence of rat class I alcohol dehydrogenase gene

An mRNA amplification procedure with directional cDNA cloning and strand-specific cRNA synthesis for comprehensive gene expression analysis

We developed an integrated system suitable for comprehensive gene expression studies including construction and analysis of cDNA microarrays starting from a small amount of mRNA. We amplified total mRNA first as cDNA mixtures by polymerase chain reaction and then as strand-specific cRNA mixtures by in vitro transcription. These amplified cDNA and cRNA enabled determination of mRNA levels by hybridization analyses such as Southern, Northern, reverse-Northern macroarray, and cDNA microarray analyses, as well as construction of the cDNA library with a unidirectional cDNA insert. By using strand-specific cRNA derived from rat primary-cultured hepatocytes, we detected putative antisense transcripts for the metallothionein gene. cDNA microarray analysis for genes regulated by glucocorticoids and glucagon in the hepatocytes revealed that a number of genes involved in signal transduction and transcriptional regulation were up- or down-regulated. The present system is widely applicable to gene expression analysis with limited amounts of RNA samples.

Post-transcriptional Regulation of Sterol Regulatory Element-binding Protein-1 by Ethanol Induces Class I Alcohol Dehydrogenase in Rat Liver

Members of the sterol regulatory element-binding protein (SREBP) family of transcription factors control the synthesis and uptake of cholesterol, fatty acids, triglycerides, and phospholipids. Continuous intragastric infusion of ethanol-containing diets as part of total enteral nutrition generates well defined 6-day cycles (pulses) of urine ethanol concentrations (UECs) in rats. Pulsatile UECs are the result of cyclical expression and activity of the principal alcohol-metabolizing enzyme, hepatic Class I alcohol dehydrogenase (ADH), and this mechanism involves regulated CCAAT/enhancer-binding protein-beta expression and binding to the ADH promoter. In this study, we further explore the molecular mechanism for ethanol-induced ADH expression during the UEC pulse in adult male rats fed ethanol by total enteral nutrition for 21-30 days. In hypophysectomized rats, in which the ADH protein increased by approximately 6-fold, the nuclear form of SREBP-1 decreased by approximately 7-fold. Because the ADH promoter contains two canonical sterol response element (SRE) sites (-63 to -53 and -52 to -40 relative to the transcription start site), electrophoretic mobility shift assays were conducted using an ADH-specific SRE site. Hepatic nuclear protein binding decreased by 2.4-fold on the ascending limbs and by 3.6-fold on the descending limbs of UEC pulses (p < 0.05). The specificity of nuclear protein binding to the ADH-SRE site was confirmed using antibody and UV cross-link assays. The in vivo binding status of SREBP-1 to ADH-SRE sites, as measured by the chromatin immunoprecipitation assay, had a pattern very similar to the electrophoretic mobility shift assay results. Functional analysis of the ADH-SREs demonstrated these sites to be essential for ADH transcription. In vitro transcription assays demonstrated that depletion of the SREBP-1 protein from nuclear extracts increased transcription activity by approximately 5-fold and that the liver X receptor agonist T0901317 (a known activator of SREBP-1c transcription) reduced in vitro expression of ADH mRNA by 2-fold. We conclude that SREBP-1 is a negative regulator of the ADH gene and may work in concert with the CCAAT/enhancer-binding proteins to mediate ethanol induction of ADH in vivo.

Early Experience and Sex Interact to Influence Limbic-Hypothalamic-Pituitary-Adrenal-Axis Function After Acute Alcohol Administration in Rhesus Macaques (Macaca mulatta)

BACKGROUND

Studies in rodents demonstrate sex differences in neuroendocrine stress axis activity after treatment with alcohol. In abstinent alcoholics, atypical depressives, and individuals with posttraumatic stress disorder, limbic-hypothalamic-pituitary-adrenal (LHPA)-axis activity is often blunted; among females in these patient populations, however, resistance to glucocorticoid feedback and increased pituitary reactivity is observed. Early parental loss is a major life stressor and is a risk factor for both affective disturbances and LHPA-axis abnormalities later in life. We wanted to determine whether sex and early life parental absence would interact to influence alcohol-induced alterations in LHPA-axis activity after exposure to ethanol in macaques.

METHODS

Animals were reared with their mothers in social groups (MR, n = 94) or without adults in peer-only groups (PR, n = 79). At 5 years of age, they received an intravenous infusion of alcohol (2-2.2 g/kg), and the effects of alcohol, sex, and rearing condition on ACTH and cortisol levels were analyzed by ANOVA.

RESULTS

Peer-reared females had higher ACTH levels than did PR males, MR females, and MR males after alcohol infusion. Alcohol-induced cortisol levels were not affected by sex and rearing condition.

CONCLUSIONS

These findings suggest that there are sex differences in glucocorticoid negative feedback, pituitary responsivity, or release of ACTH secretagogues among individuals exposed to early life stress and emphasize the importance of considering sex effects when studying LHPA-axis dysregulation in alcoholism and other stress-related neuropsychiatric disorders.

Ethanol induction of class I alcohol dehydrogenase expression in the rat occurs through alterations in CCAAT/enhancer binding proteins beta and gamma

Alcohol dehydrogenase (ADH) is the principal ethanol-metabolizing enzyme. Ethanol induces rat Class I ADH mRNA and activity by an as yet unknown mechanism. In the current study, adult male rats were fed an ethanol-containing diet by continuous intragastric infusion for 42 days. Hepatic Class I ADH mRNA, protein, and activity levels in the ethanol-infused rats increased 3.9-, 3.3-, and 1.7-fold, respectively (p <0.05). Cis-acting elements within the proximal promoter region of the ADH gene were studied by electrophoretic mobility shift assay (EMSA). Hepatic nuclear extract (HNE) binding to either the consensus or ADH-specific CCAAT/enhancer binding protein (C/EBP) sites was >2.4-fold greater in ethanol-fed rats (p <0.05) than controls. Antibody-specific EMSA assays demonstrated binding of the transcription factor C/EBPbeta to the C/EBP site. Western blot immunoblot analysis of HNEs demonstrated 3.5- and 2.3-fold increases in C/EBPbeta (LAP) and C/EBPdelta (p <0.05), respectively, in ethanol-fed rats compared with controls, whereas levels of the truncated C/EBPbeta (LIP) and C/EBPgamma were lower in ethanol-fed rats (p <0.05). HNE from ethanol-fed rats increased (3-fold) the in vitro transcription of rat Class I ADH (p <0.05), and mutation of the C/EBP element in the proximal promoter region blocked this effect. Antisera against LIP or C/EBPgamma enhanced transcription efficiency (p <0.05). These data provide the first evidence for the mechanism by which ethanol regulates rat hepatic Class I ADH gene expression in vivo. This mechanism involves the C/EBP site and the enhancer binding proteins beta and gamma.

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.

Transcriptional control of the murine polymeric IgA receptor promoter by glucocorticoids

Glucocorticoids have been implicated as an important regulator of intestinal epithelial cell ontogeny. The polymeric IgA receptor (pIgR) is expressed in the intestinal epithelial layer and is regulated by several mediators, including glucocorticoids. The mechanism of how corticosteroids alter the transcriptional regulation of pIgR expression has not been defined. In this study, we demonstrated that glucocorticoids upregulate steady-state pIgR mRNA levels in the proximal intestine of suckling rats and in the IEC-6 intestinal cell line. We performed functional analysis of the 5'-flanking region in the presence of glucocorticoids and its receptor using the intestinal cell line Caco-2. We screened 4.7 kb of the upstream region of the murine gene and identified the most potent steroid response element to reside between nt -215 and -163 relative to the start of transcription. Substitution mutation analysis of this region identified the location of the putative steroid response element to be between nt -195 and -176. In vitro DNase I footprint analysis using the recombinant glucocorticoid receptor DNA binding domain confirmed a single area of protection that spans the nt identified by mutagenesis analysis. Electrophoretic mobility shift assays of the putative element confirmed the binding of both recombinant and cell synthesized glucocorticoid receptor in a specific manner. In summary, we report the identification and characterization of the glucocorticoid-DNA response element located in the immediate 5'-upstream region of the murine pIgR gene.

Primary sequence of the human, lysine-rich, ribosomal protein RPL38 and detection of an unusual RPL38 processed pseudogene in the promoter region of the type-1 angiotensin II receptor gene

We have isolated a cDNA clone encoding the human ribosomal protein L38 (HSRPL38). The longest ORF of the cDNA predicts a lysine-rich small polypeptide identical to the rat RPL38 protein (100% identity), and sharing a 84% of identity to the tomato RPL38 protein sequence. Northern blot analysis of a number of epithelial cell lines showed that the HSRPL38 is encoded by a mRNA ubiquitously expressed. Southern blot analysis of human genomic DNA suggested that the RPL38 does not constitute a multigene family but it is encoded by a reduced set of active genes, among which we have also found a RPL38 processed pseudogene located in the promoter region of the human type-1 angiotensin II receptor gene. This RPL38 pseudogene is very unusual among processed pseudogenes in that the poly A tail and the entire 5'-UTR of the original RPL38 mRNA were deleted during the retrotransposition process.

Methylation sensitive protein binding to an intragenic active X-specific methylated region in the M. robustus Hprt gene

An intragenic region of the wallaroo (Macropus robustus) hypoxanthine phosphoribosyltransferase gene which contains three active X-specific methylated cytosines was examined for protein(s) binding. In vitro DNase I footprinting of unmethylated DNA identified three footprints, one of which (footprint I) contained two of the known differentially methylated sites (a HpaII and a HhaI site). Methylation of the footprint I HpaII site only, abolished the formation of several, specific DNA-protein complexes in mobility shift assays. UV cross-linking experiments indicated that polypeptides involved in the methylation sensitive interactions with footprint I had molecular weights ranging from 72 to 48 kDa. Analogous results were obtained with nuclear extracts from both eutherian and metatherian cells, indicating that these proteins are conserved. We suggest that the binding of these proteins to the inactive X may play some role in gene silencing, with the active gene being protected from this effect by methylation of the binding site.

The expression of mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme-A synthase in neonatal rat intestine and liver is under transcriptional control

Mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HOMeGlt-CoA) synthase regulates ketogenesis in the liver of adult rat and in the intestine and liver of neonatal animals but whose mechanisms of regulation have not been fully defined. To investigate transcriptional control of this gene in intestine and liver of suckling rats a quantitative PCR amplification of the pre-mRNA (heteronuclear RNA), compose of part of the first exon and of the first intron, was carried out. Results show that the intestinal pre-mRNA for mitochondrial HOMeGlt-CoA synthase from suckling rats follows a pattern that is nearly identical to that of mature mRNA, with maximum levels on the ninth postnatal day then decreasing smoothly so that at weaning there is no transcriptional activity. Mitochondrial HOMeGlt-CoA synthase protein follows a pattern that is identical to the pre-mRNA and mature mRNA, suggesting no translational regulation. The changes in transcriptional activity are not produced by the presence of an alternative promoter, since the transcription-initiation site is identical in several tissues assayed, including intestine and liver. Enterocytes are the only intestinal cells that express this ketogenic enzyme, as deduced from immunolocalization experiments. The mature intestinal protein is located in mitochondria and not in the cytosol, which coincides with what is found in liver. By using analogous techniques we conclude that hepatic pre-mRNA of mitochondrial HOMeGlt-CoA synthase from suckling rats follows a pattern of expression identical to that of mature hepatic mRNA, which also suggests a transcriptional modulation of this gene in the liver of neonatal rats.

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.

Promoter regulation of a differentially expressed gene in the human colonic epithelial cell lines HT29-18 and HT29-18-C1

Gene A4 is transcriptionally activated upon enterocyte differentiation of the human colonic epithelial cell line HT29-18 and its highly differentiated subclone HT29-18-C1 [Oliva et al., Arch. Biochem. Biophys. 302 (1993) 183-192]. To characterize the mechanisms regulating the differential transcription of A4, we analyzed its immediate 5'-flanking region for regulatory elements. Promoter-linked transfection experiments of progressively deleted A4 5'-flanking sequences fused to the bacterial cat reporter gene suggest the presence of one negative and two positive DNA elements within the first 371 bp of the A4 promoter (pA4). DNase I footprint and electrophoretic mobility shift assays demonstrate that one positive element which contains the core binding sequence for the transcription factor, Sp1, mediates an equal level of transcription in the two cell types. The second positive element, localized between nucleotide positions--169 and -152, contains a sequence previously unrecognized as a transcription factor-binding site. This element mediates a twofold increase in the activity of pA4 in HT29-18-C1, as compared to HT29-18. Furthermore, nuclear extracts obtained from HT29-18-C1 contain a higher binding activity for this element than those from HT29-18. Southwestern blot analysis suggests that the protein interacting with this element has an estimated molecular mass of 50 kDa. We conclude that this protein may be involved in the differential regulation of A4 in these intestinal cell lines.