Beyond Watson and Crick: DNA methylation and molecular enzymology of DNA methyltransferases

Involvement of the DNA Phosphorothioation System in TorR Binding and Anaerobic TMAO Respiration in Salmonella enterica

Although the phosphorothioate (PT) modification, in which the nonbridging oxygen in the DNA sugar-phosphate backbone is replaced by sulfur, has been reported to play versatile roles in multiple cellular processes, very little data have been obtained to define the role of PT in epigenetic regulation. In this study, we report that the PT system in Salmonella enterica serovar Cerro 87 is involved in the transcriptional regulation of the torCAD operon encoding the trimethylamine N-oxide (TMAO) respiration machinery that enables the use of TMAO as a terminal electron acceptor for respiration when oxygen is not available. In vitro, PT enhanced the binding of the transcriptional activator of the torCAD operon, namely, TorR, to its DNA substrate (tor boxes). However, in vivo, the PT modification protein complex DndCDE downregulated torCAD transcription through competing with the binding of TorR to the tor boxes. The altered expression of torCAD caused by PT modification proteins affected cell growth that relied on TMAO respiration. To our knowledge, this is the first report supporting that PT proteins participate in transcriptional regulation, showing a new function of PT systems.

Mechanism and biological role of Dnmt2 in Nucleic Acid Methylation

A group of homologous nucleic acid modification enzymes called Dnmt2, Trdmt1, Pmt1, DnmA, and Ehmet in different model organisms catalyze the transfer of a methyl group from the cofactor S-adenosyl-methionine (SAM) to the carbon-5 of cytosine residues. Originally considered as DNA MTases, these enzymes were shown to be tRNA methyltransferases about a decade ago. Between the presumed involvement in DNA modification-related epigenetics, and the recent foray into the RNA modification field, significant progress has characterized Dnmt2-related research. Here, we review this progress in its diverse facets including molecular evolution, structural biology, biochemistry, chemical biology, cell biology and epigenetics.

Clinical significance and association of caveolin-1 and Dnmt1 gene with carcinogenesis, development of gastric carcinomas

AIM: To investigate the expression of caveolin-1and Dnmt1 genes in normal gastric mucosa and gastric carcinoma, and to detect methylation status of CpG island of caveolin-1 gene promoter region located in exon 1 and its clinical significance in gastric carcinoma.

METHODS: Methylation status of caveolin-1 gene in 60 gastric carcinoma cases and 14 normal gastric tissues was detected using Methylation-specific PCR (MSP). SP immunohistochemcal method and in site hybridization (ISH) were used to detect the expression of caveolin-1 protein and Dnmt1 protein and mRNA.

RESULTS: The methylation rate of the 5' CpG island of caveolin-1 gene was 0% in 14 normal gastric tissues, and 73.3% in 60 gastric carcinoma cases. There was significant difference between two groups (P < 0.005). Methylation status of caveolin-1 gene was related to the patient's age. The positive rates of caveolin-1 protein, Dnmt1 protein and mRNA were 30%, 63.3% and 53.3% in 60 gastric carcinoma cases.

CONCLUSION: The methylation and inactivation of caveolin-1 gene leads to carcinogenesis and development of gastric carcinomas by the function of Dnmt1 gene.