The altered DNA methylation pattern and its implications in liver cancer.

DNA methylation is the most intensively studied epigenetic phenomenon, disturbances of which result in changes in gene transcription, thus exerting drastic imparts onto biological behaviors of cancer. Both the global demethylation and the local hypermethylation have been widely reported in all types of tumors, providing both challenges and opportunities for a better understanding and eventually controlling of the malignance. However, we are still in the very early stage of information accumulation concerning the tumor associated changes in DNA methylation pattern. A number of excellent recent reviews have covered this issue in depth. Therefore, this review will summarize our recent data on DNA methylation profiling in cancers. Perspectives for the future direction in this dynamic and exciting field will also be given.

A novel protein-DNA interaction involved with the CpG dinucleotide at -30 upstream is linked to the DNA methylation mediated transcription silencing of the MAGE-A1 gene.

To understand the DNA-methylation mediated gene silencing mechanisms, we analyzed in cell culture of the promoter function of the MAGE-A1 gene, which is frequently demethylated and over-expressed in human hepatocellular carcinoma. We have established the correlation of the DNA methylation of the promoter CpG island with expression status of this gene in a panel of the established liver cancer cell lines. The crucial CpG dinucleotide(s) within the minimal promoter subjected to the control mediated by DNA methylation with profound biological functions was also delineated. Furthermore, a novel sequence-specific DNA-protein interaction at the -30 CpG dinucleotide upstream of the gene was found having a vital part to play in the DNA methylation mediated transcription silencing of the MAGE-A1 gene. Our results would not only provide new insights into the DNA methylation mediated mechanisms over transcription of the MAGE-A1 gene, but also pave the way for further defining the cross-talk among DNA methylation, histone modification and chromatin remodeling in detail.

The ATF/CREB site is the key element for transcription of the human RNA methyltransferase like 1(RNMTL1) gene, a newly discovered 17p13.3 gene.

The human RNA methyltransferase like 1 gene (RNMTL1) is one of thirteen newly discovered genes within a 116 Kb segment of the chromosome 17p13.3 that suffers from a high frequent loss of heterozygosity in human hepatocellular carcinoma in China[1-5]. To understand the molecular mechanisms underlying transcription control of the RNMTL1 gene in human cancers, we decline using of the conventional approach where the cis-elements bound by the known transcription factors are primary targets, and carried out the systematic analyses to dissect the promoter structure and identify/characterize the key cis-elements that are responsible for its strong expression in cell. The molecular approaches applied included 1, the primer extension for mapping of the transcription starts; 2, the transient transfection/reporter assays on a large number of deletion and site-specific mutants of the promoter segment for defining the minimal promoter and the crucial elements within; and 3, the electrophoresis mobility shift assay with specific antibodies for reconfirming the nature of the transcription factors and their cognate cis-elements. We have shown that the interaction of an ATF/CREB element (-38 to -31) and its cognate transcription factors play a predominant role in the promoter activity of the RNMTL1 gene. The secondary DNA structures of the ATF/CREB element play a more vital role in the protein-DNA interaction. Finally, we reported a novel mechanism underlying the YY1 mediated transcription repression, namely, the ATF/CREB dependent transcription-repression by YY1 is executed in absence of its own sequence-specific binding.

The promoter analysis of the human C17orf25 gene, a novel chromosome 17p13.3 gene.

The human C17orf25 gene (Accession No. AF177342) is one of thirteen genes cloned from a region displaying a high score of loss of heterozygosity within chromosome 17p13.3 in human hepatocellular carcinoma in China. To unveil the underlying mechanisms for the transcription regulation of this gene and understand its implication to the hepatocellular carcinogenesis, we looked into the relevant aspects by both bioinformatic and experimental executions. We found: 1, The abundant expression of the C17orf25 gene was evident in all the cell lines and tissue samples tested, showing little hepatoma-selectivity; 2, Its transcription starts at a single site, locating at -60 from the translation initiation codon; 3, A 58 bp fragment containing the transcription start, extending from -112 to -55, represents the minimal promoter; 4, The consensus sequence within this fragment recognized by SP1 contributes predominantly to the activity of the minimal promoter; 5, The bioinformatic analysis suggests that the C17orf25 gene may encode a protein in the family of the glyoxalase. Our data has provided some deep insight into both function and regulation of the C17orf25 gene in the context of the normal liver and hepatocellular carcinoma.