Silencing and CpG island methylation of GSTP1 is rare in ordinary gastric carcinomas but common in Epstein-Barr virus-associated gastric carcinomas.

BACKGROUND: The GSTPI gene encodes for glutathione S-transferase pi (GST-pi), which protects cells from cytotoxic agents. The carcinogenic role of this enzyme is at issue because functional polymorphisms have been shown to be a risk factor of human cancer. Moreover, GST-pi protein loss has frequently been reported in various human cancers.
MATERIALS AND METHODS: The expression of GST-pi and the methylation status of the promoter area of GST-pi were investigated in gastric carcinomas. Eleven human SNUgastric cancer cell lines, PC-3 prostate cancer cell lines, various cancer tissues and normal gastric mucosa tissues were analyzed by immunohistochemistry, in situ hybridization, Western blot and methylation specific PCR.
RESULTS: Only 22 (2.0%o) out of 1081 cases showed loss of GST-pi expression. Interestingly, 16 out of 22 GST-pi-negative cases were Epstein-Barr virus (EBV)-associated gastric carcinomas. The loss of expression of GST-pi among EBV-associated gastric carcinomas was found to be 27.1% (16/59), but to be 0.6% (6/1022) in EBV-negative gastric carcinomas (p < 0.001). Eight out of 16 cases with loss of GST-pi expression showed CpG island methylation in the GSTP1 promoter region, while none of the normal gastric mucosa or EBV-negative gastric carcinomas showed methylation (p < 0.001).
CONCLUSION: These findings demonstrate that the loss of GST-pi expression is clustered in a subset of gastric carcinomas with EBV incorporation, and that the methylation of the promoter of the GSTP1 gene is correlated with this loss of GST-pi expression. Our results suggest that GST-pi abrogation by CpG island hypermethylation may account for EBV-associated gastric carcinoma.