Silencing of GSTP1 gene by CpG island DNA hypermethylation in HBV-associated hepatocellular carcinomas

S Zhong, PhD, W Yeo, MD, MW Tang, C Liu, YMD Lo, MD, and PJ Johnson, MD.

The Chinese University of Hong Kong, Hong Kong Sar, China

We assess the role of epigenetic silencing of the GSTP1 gene, a gene encoding the pi-class glutathione S-transferase, in the pathogenesis of HBV-associated hepatocellular carcinomas (HCC). The cell lines Hep3B, HepG2 and a cohort of 43 HBV-associated HCC tissue specimens and corresponding non-tumor tissues were subjected to analysis for GSTP1 epigenetic alteration and expression. GSTP1 'CpG' island DNA hypermethylation in the liver cell lines and the tissue specimens were determined by methylation specific PCR (MSP) and correlated with expression of the gene using reverse-transcription PCR (RT-PCR), immuno-blotting and immunohistochemistry (IHC). GSTP1 'CpG island' DNA hypermethylation was detected in 28 of 43 (65.1%) HCC tissues and 4 of 40 (10%) corresponding non-tumor tissues. GSTP1 protein was absent in those cases showing hypermethylation of the gene. Similarly, DNA from Hep3B and HepG2 cell lines displayed complete GSTP1 hypermethylation in the 'CpG' island and they failed to express GSTP1 mRNA and the corresponding protein product. Treatment of the cell lines with the DNA methyltransferase inhibitor 5-aza-deoxycytidine reversed the hypermethylation and restored GSTP1 mRNA and polypeptide expression. These data indicate that epigenetic silencing of GSTP1 gene expression by 'CpG island' DNA hypermethylation is common in human HBV-associated HCC. In addition, somatic GSTP1 inactivation, via 'CpG island' hypermethylation may contribute to the pathogenesis of this malignancy.

KEY WORDS: Methylation, Hepatocellular Carcinomas.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Prevention.

This presentation received an honorable mention in our poster contest and was recognized with the Symposium Presidents' Award for Scientific Excellence.