Hypermethylation of metallothionein-3 CpG island in gastric carcinoma.

Deng D, El-Rifai W, Ji J, Zhu B, Trampont P, Li J, Smith MF, Powel SM
Carcinogenesis. 2003 24 (1): 25-9

PMID: 12538345 · DOI:10.1093/carcin/24.1.25

The expression of metallothionein (MT)-3 is often markedly reduced in gastric carcinoma (GC). The molecular mechanism of this MT-3 downregulation is unknown. Transcriptional silencing of MT-3 by methylation of CpG island was investigated by nucleotide sequencing and denaturing high performance liquid chromatography (DHPLC) analyses. We found that normal brain tissue and a xenografted GC that expressed MT-3 mRNA had unmethylated regions of the CpG island in intron1 of this gene. On the other hand, gastric cancer cell lines AGS and MKN445, a xenografted GC, and a representative primary gastric cancer that had no expression of MT-3 mRNA demonstrated hypermethylation of the MT-3 intron1 CpG island. Treatment of the gastric cancer cell lines with 5-azacytidine resulted in new expression of MT-3 mRNA in these cells. A quantifying DHPLC assay was developed to determine the methylation status of this specific region of the MT-3 gene. Fifty-eight primary GC and their corresponding normal gastric epithelial tissues, and 34 normal gastric mucosa were analyzed for MT-3 methylation by DHPLC in the region of methylation abnormalities initially identified. Our DHPLC analyses of the methylated MT-3 product demonstrated that the primary gastric cancers have an average methylation percentage of 6.3% per tumor compared with 2.4% in normal gastric tissues (P < 0.05). The MT-3 was not methylated in all of eight P53-positive GCs and hypermethylated in eight of 13 P53-negative cases by immunohistochemistry staining (P = 0.007). In conclusion, the CpG island in the MT-3 intron1 are abnormally hypermethylated in many gastric carcinomas and may account for the downregulation of MT-3 in gastric carcinogenesis.

MeSH Terms (18)

Adult Aged Aged, 80 and over Animals Brain CpG Islands DNA Methylation Female Humans Introns Male Mice Middle Aged Nerve Tissue Proteins Reverse Transcriptase Polymerase Chain Reaction RNA, Messenger Stomach Neoplasms Tumor Cells, Cultured

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