Tissue- and developmental-stage-specific methylation in the two kidney promoters of the rat gamma-glutamyl transpeptidase gene

Expression of cholecystokinin type A receptor gene correlates with DNA demethylation during postnatal development of rat pancreas

Cholecystokinin stimulates pancreatic amylase secretion, gallbladder contraction, and pancreatic growth, etc. by binding with high affinity to a cholecystokinin type A receptor (CCKAR). To better understand the expression of CCKAR mRNA in terms of tissue specificity and postnatal development, we determined the methylation status of BssHII sites (5'-B sites) in the rat CCKAR gene promoter. The 5'-B sites in adult pancreas expressing CCKAR mRNA were much less extensively methylated than those in fetal pancreas not expressing the mRNA. In brain, liver, and kidney of adult rats not expressing CCKAR mRNA, the 5'-B sites were methylated. In pancreas, the demethylation level of the sites increased at 21 days after birth. Concomitant with the DNA demethylation level in the 5'-B sites, the mRNA level rose rapidly in 21 days. These results demonstrate that methylation and expression of the CCKAR gene reveal a good inverse correlation.

gamma-Glutamyl transpeptidase: catalytic mechanism and gene expression

The gamma-glutamyl transpeptidases are key enzymes in the so-called gamma-glutamyl cycle involving glutathione synthesis, the recovery of its constituents, and in the transport of amino acids. This membrane-bound ectoenzyme thus serves to regulate glutathione synthesis. This chapter deals with the active site chemistry of gamma-glutamyl transpeptidase, including the role of side-chain groups on the light subunit as well as several serine residues in the catalytic process. Also considered are genomic studies indicating (a) the presence of a single gene in mouse and rat; (b) the occurrence of multiple genes in humans; (c) the involvement of multiple promoters for gene expression; and (d) how these multiple promoters may play a role in the tissue-specific expression of gamma-glutamyl transpeptidases.

Tissue-specific methylation occurs in the essential promoter element of the tyrosine hydroxylase gene

Expression of tyrosine hydroxylase (TH) is regulated in a tissue-specific manner by multiple mechanisms. In catecholaminergic cells, the expression of TH-mRNA is up-regulated by forskolin (FK) and is suppressed by retinoic acid (RA). We have previously provided evidence that, in N-18 cells, the expression of TH-mRNA is suppressed by DNA methylation of the TH gene itself. In the present study, using a catecholaminergic cell line, N1E-115, we performed deletional and mutational analyses on the 5'-flanking region of the mouse TH gene. The results indicate that a cAMP response element (CRE) mediates constitutive transcription of the TH gene, as well as responsiveness to FK and RA. Using bisulfite sequencing methods, we analyzed the methylation status of the TH gene 5'-flanking region in various cell lines and rat tissues. We found that three cytosine residues in the domain surrounding the CRE of the TH gene promoter were specifically methylated in N-18 cells and TH non-expressing rat tissues. In contrast, these cytosines were undermethylated in TH expressing cell lines and tissues. The inverse correlation between the frequency of cytosine methylation at these specific sites and the levels of TH expression supports a role for DNA methylation in the regulation of tissue-specific gene expression.

The 5' untranslated region of the human gamma-glutamyl transferase mRNA contains a tissue-specific active translational enhancer

We report the functional and structural analysis of the 5' untranslated region (5'UTR) of human hepatoma HepG2 gamma-glutamyltransferase (GGT) mRNA. Transient expression of a hybrid GGT-luciferase gene in HepG2, MIA-Pa-Ca-2 and MG 63 cell lines shows that this 5'UTR acts as a tissue-specific translational enhancer. Evidence for transcripts with multiple 5'UTR coding for HepG2 GGT was obtained by RNase protection. Computer analysis of this 5'UTR detected the existence of a stable stem and loop structure containing multiple steroid modulatory elements.