A negative regulatory element upstream from the mouse Adh-1 gene can down-regulate a heterologous promoter

Regulation of ethanol-related behavior and ethanol metabolism by the Corazonin neurons and Corazonin receptor in Drosophila melanogaster

Impaired ethanol metabolism can lead to various alcohol-related health problems. Key enzymes in ethanol metabolism are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH); however, neuroendocrine pathways that regulate the activities of these enzymes are largely unexplored. Here we identified a neuroendocrine system involving Corazonin (Crz) neuropeptide and its receptor (CrzR) as important physiological regulators of ethanol metabolism in Drosophila. Crz-cell deficient (Crz-CD) flies displayed significantly delayed recovery from ethanol-induced sedation that we refer to as hangover-like phenotype. Newly generated mutant lacking Crz Receptor (CrzR(01) ) and CrzR-knockdown flies showed even more severe hangover-like phenotype, which is causally associated with fast accumulation of acetaldehyde in the CrzR(01) mutant following ethanol exposure. Higher levels of acetaldehyde are likely due to 30% reduced ALDH activity in the mutants. Moreover, increased ADH activity was found in the CrzR(01) mutant, but not in the Crz-CD flies. Quantitative RT-PCR revealed transcriptional upregulation of Adh gene in the CrzR(01) . Transgenic inhibition of cyclic AMP-dependent protein kinase (PKA) also results in significantly increased ADH activity and Adh mRNA levels, indicating PKA-dependent transcriptional regulation of Adh by CrzR. Furthermore, inhibition of PKA or cAMP response element binding protein (CREB) in CrzR cells leads to comparable hangover-like phenotype to the CrzR(01) mutant. These findings suggest that CrzR-associated signaling pathway is critical for ethanol detoxification via Crz-dependent regulation of ALDH activity and Crz-independent transcriptional regulation of ADH. Our study provides new insights into the neuroendocrine-associated ethanol-related behavior and metabolism.

A tetracycline-regulated adenoviral expression system for in vivo delivery of transgenes to lung and liver

BACKGROUND

Recombinant adenoviruses are an established tool for somatic gene transfer to multiple cell types in animals as well as in tissue culture. However, generation of adenoviruses expressing transgenes that are potentially toxic to the host cell line represents a practical problem. The aim of this study was to construct an adenoviral expression system that prevents transgene expression during the generation and propagation of the virus, and allows efficient gene transfer to lung and liver, major target organs of gene therapy.

METHODS

Using the tet-off system we constructed tetracycline (tet) regulatable recombinant adenoviruses expressing the marker gene LacZ (Adtet-off.LacZ) as well as a secretory protein, human group IIA secretory phospholipase A(2) (Adtet-off.hsPLA(2)). Expression (Western blot, activity assay) was tested in vitro (HeLa cells), and in vivo by gene transfer to lung and liver.

RESULTS

Without addition of tetracycline we demonstrated expression of LacZ (Adtet-off.LacZ) and sPLA(2) (Adtet-off.hsPLA(2)) in HeLa cells. Providing additional tet-transactivator (tTA) protein either by stable transfection or coinfection with a tTA-expressing adenovirus resulted in a further increase of LacZ and sPLA(2) expression. Transgene expression in vitro was eliminated by the addition of tetracycline to the culture medium. Adtet-off.LacZ and Adtet-off.hsPLA(2) allowed successful gene transfer in vivo to lung and liver. While the expression was highly efficient within the lungs, however, additional tTA was necessary to achieve high-level expression within liver.

CONCLUSIONS

Tet-regulatable adenoviral expression systems may facilitate the construction of recombinant adenoviruses encoding potentially toxic transgenes and permit regulated transgene expression.

Distal and proximal cis-linked sequences are needed for the total expression phenotype of the mouse alcohol dehydrogenase 1 (Adh1) gene

Mouse alcohol dehydrogenase 1 (Adh1) gene expression occurs at high levels in liver and adrenal, moderate levels in kidney and intestine, low levels in a number of other tissues, and is undetectable in thymus, spleen and brain by Northern analysis. In transgenic mice, a minigene construct containing 10 kb of upstream and 1.5 kb of downstream flanking sequence directs expression in kidney, adrenal, lung, epididymis, ovary and skin but promotes ectopic expression in thymus and spleen while failing to control expression in liver, eye, intestine and seminal vesicle. Cosmids containing either 7 kb of upstream and 21 kb of downstream or 12 kb of upstream and 23 kb of downstream sequence flanking genetically marked Adh1 additionally promotes seminal vesicle expression suggesting downstream or intragenic sequence controls expression in this tissue. However, expression in liver, adrenal, or intestine is not promoted. The Adh1(a) allele on the cosmid expresses an enzyme electrophoretically distinct from that of the endogenous Adh1(b) allele, and presence of the heterodimeric enzyme in expressing tissues confirms that transgene activity occurs in the same cell-type as the endogenous gene. Transgene expression levels promoted by cosmids were at physiologically relevant amounts and exhibited greater copy-number dependence than observed with minigenes. Transgene mRNA expression correlated with expression measured at the enzyme level. A bacterial artificial chromosome containing 110 kb of 5'- and 104 kb of 3'-flanking sequence surrounding the Adh1 gene promoted expression in tissues at levels comparable to the endogenous gene most importantly including liver, adrenal and intestinal tissue where high level Adh1 expression occurs. Transgene expression in liver was in the same cell types as promoted by the endogenous gene. Although proximal elements extending 12 kb upstream and 23 kb downstream of the Adh1 gene promote expression at physiologically relevant levels in most tissues, more distal elements are additionally required to promote normal expression levels in liver, adrenal and intestinal tissue where Adh1 is most highly expressed.

Identification and expression of cosmids with an allelic variant of class I alcohol dehydrogenase in transgenic mice

The mouse Adh1 gene exhibits tissue-specific regulation, is developmentally regulated, and is androgen regulated in kidney and adrenal tissue. To study this complex regulation phenotype a transgenic mouse approach has been used to investigate regulatory regions of the gene necessary for proper tissue expression and hormonal control. Transgenic mice have been produced with an Adh1 minigene as a reporter behind either 2.5- or 10 kb of 5'-flanking sequence [1]. Complete androgen regulation in kidney requires a region between -2.5 and -10 kb. A sequence extending to -10 kb does not confer liver expression in this minigene construct. B6.S mice express an electrophoretically variant protein resulting from a known nucleotide substitution resulting in a restriction endonuclease length polymorphism. Transgenic mice harboring B6.S cosmids can be studied for expression analysis at both protein and mRNA levels, identification of transgenic founders and inheritance studies are greatly facilitated by a PCR-restriction endonuclease cleavage approach, the entire mouse gene is used as a reporter, and the formation of heterodimeric enzyme molecules can be used to infer expression of the transgene in the proper cell types within a given tissue. Expression of a B6.S cosmid containing the entire Adh1 gene and 6 kb of 5'- and 21 kb of 3'-flanking region occurs in transgenic mice in a copy number dependent manner in a number of tissues, but expression in liver does not occur. The ability to analyze expression at the protein and mRNA levels has been confirmed using this system. Future directions will involve the use of large BAC clones modified by RARE cleavage to identify the liver specific elements necessary for expression.

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 regulation of the rat poly(ADP-ribose) polymerase gene by Sp1

Expression of the gene encoding poly(ADP-ribose) polymerase (PARP), although ubiquitous, nevertheless varies substantially between tissues. We have recently shown that Sp1 binds five distinct target sequences (US-1 and F1-F4) in the rat PARP (rPARP) gene promoter. Here we used deletion analyses and site-directed mutagenesis to address the regulatory function played by these Sp1 sites on the basal transcriptional activity directed by the rPARP promoter. Transfection experiments revealed that the most proximal Sp1 site is insufficient by itself to direct any promoter activity. In addition, a weak negative regulatory element was identified between positions -101 and -60. The rPARP promoter directed high levels of chloramphenicol acetyltransferase activity in Jurkat T-lymphoblastoid and Ltk- fibroblast cells but only moderate levels in pituitary GH4C1 and liver HTC cells, correlating with the amounts of PARP detected in these cells by western blot analysis. However, the reduced promoter efficiency in HTC and GH4C1 cells did not result from the lack of Sp1 activity in these cells but suggested that yet uncharacterized regulatory proteins might turn off PARP gene expression by binding negative regulatory elements from the rPARP promoter. Similarly, site-directed mutagenesis on the three most proximal Sp1 elements suggested the influence exerted by Sp1 on the rPARP promoter activity to vary substantially between cell types. It also provided evidence for a basal rPARP promoter activity driven through the recognition of unidentified cis-acting elements by transcription factors other than Sp1.

The rat growth hormone and human cellular retinol binding protein 1 genes share homologous NF1-like binding sites that exert either positive or negative influences on gene expression in vitro

High levels of expression for the rat growth hormone (rGH) gene are restricted to the somatotroph cells of the anterior pituitary. Previously, we have shown that rGH cell-specific repression results in part from the recognition of negatively acting silencers by a number of nuclear proteins that repress basal promoter activity. Examination of these silencers revealed the presence of binding sites for proteins that belong to the NF1 family of transcription factors. Indeed, proteins from this family were shown to bind the rGH proximal silencer (designated silencer-1) in in vitro assays. Furthermore, this silencer site is capable of repressing chloramphenicol acetyltransferase (CAT) gene expression driven by an heterologous promoter (that of the mouse p12 gene), even in pituitary cells. Recently, we identified in the 5' untranslated region of the gene encoding human cellular retinol binding protein 1 (hCRBP1) a negative regulatory element (Fp1) that also bears an NF1 binding site very similar to that of rGH silencer-1. However, although deletion of Fp1 in the hCRBP1 gene yielded increased CAT activity, pointing toward a negative regulatory function exerted by this element, its insertion upstream of the p12 basal promoter results in an impressive positive stimulation of CAT gene expression. By exploiting NaDodSO4 gel protein fractionation and renaturation, we identified a 40-kD nuclear protein (designated Bp1) present in GH4C1 cells that binds very strongly to rGH silencer-1 but only weakly to hCRBP1 Fp1. Similarly, we also detected a 29-kD nuclear factor (designated Bp2) that recognizes exclusively the Fp1 element as its target site, therefore suggesting that different, but likely related, proteins bind these homologous elements to either activate or repress gene transcription. Although they bind DNA through the recognition of the NF1-like target sequence contained on these elements, competition and supershift experiments in electrophoretic mobility shift assays provided evidence that neither of these proteins belong to the NF1 family.

Ten kilobases of 5'-flanking region confers proper regulation of the mouse alcohol dehydrogenase-1 (Adh-1) gene in kidney and adrenal of transgenic mice

The expression profile of the mouse Adh-1 gene, which encodes class I alcohol dehydrogenase enzyme (ADH), is complex and includes tissue specificity and differential hormone responsiveness. Whereas kidney Adh-1 transcription rate is stimulated six- to sevenfold by testosterone treatment, adrenal gland ADH-1 mRNA is reduced to less than 5% of control level within 18 h following hormone administration. Androgen receptor is required for both responses since neither occurs in Tfm mutant mice lacking receptor. Hormonal and tissue-specific aspects of Adh-1 regulation were studied in transgenic mice harboring either of two constructs containing either -2.5 kb or -10 kb of 5'-flanking sequence attached to an Adh-1 minigene. The minigene transcript was expressed in kidney and adrenal tissues, but not liver, in five independent lines harboring a transgene with -2.5 kb of 5'-flanking sequence. Androgen treatment repressed the level of the minigene transcript in adrenal gland, but did not cause induction in kidney. In four lines of transgenic mice carrying the construct with -10 kb of 5'-flanking sequence, the minigene transcript was both repressed in adrenal and induced in kidney by testosterone. These lines have no detectable transgene expression in liver tissue. The -10 kb region in the mouse Adh-1 gene contains necessary controlling regions for proper tissue expression and hormonal regulation in kidney and adrenal; however, this region does not contain all essential elements necessary for expression in liver.