GSTP1 CpG island DNA hypermethylation in hepatocellular carcinomas

Glutathione S-transferases, enzymes that defend cells against damage mediat ed by oxidant and electrophilic carcinogens, may be critical determinants o f cancer pathogenesis. We report here that the pathogenesis of hepatocellul ar carcinoma (HCC), one of the most common cancers in the world, frequently involves an accumulation of somatic 'CpG island' DNA methylation changes a t GSTP1, the gene encoding the pi-class glutathione S-transferase. For our study, Hep3B HCC cells and a cohort of 20 HCC tissue specimens were subject ed to analysis for GSTP1 expression and for somatic GSTP1 alterations. GSTP 1 'CpG island' DNA hypermethylation in HCC DNA was assessed by Southern blo t analysis, via a polymerase chain reaction (PCR) assay, and by using a gen omic sequencing approach. Hep3B HCC cells failed to express GSTP1 mRNA or G STP1 polypeptides. Similarly, HCC cells in 19 of 20 HCC cases were devoid o f GSTP1 polypeptides. By Southern blot analysis, DNA from Hep3B HCC cells d isplayed abnormal GSTP1 'CpG island' hypermethylation. Treatment of Hep3B H CC cells in vitro with the DNA methyltransferase inhibitor 5-aza-deoxycytid ine both reversed GSTP1 'CpG island' DNA hypermethylation and restored GSTP 1 expression. Using a PCR assay, somatic GSTP1 'CpG island' DNA hypermethyl ation was also detected in HCC DNA from 17 of 20 HCC cases; Genomic sequenc ing analyses, undertaken to map 5-methyldeoxycytidine nucleotides located a t the GSTP1 transcriptional regulatory region, frequently detected somatic DNA hypermethylation near the gene promoter in HCC DNA. The data indicate t hat GSTP1 'CpG island' DNA hypermethylation changes appear frequently in hu man HCC. In addition, the data raise the possibility that somatic GSTP1 ina ctivation, via 'CpG island' hypermethylation, may contribute to the pathoge nesis of HCC.