| The π-class glutathione S-transferases (GSTs) are inducible enzymes that can detoxify carcinogenic oxidants and electrophiles. In rats, the π-class GST, GST-P, is expressed at high levels during the pathogenesis of liver cancer. This leads to a model whereby rats are able to elude to chemotoxic effects of carcinogens in the liver. In humans, the π-class GST, GSTP1, is most often not expressed during the pathogenesis of liver cancer, perhaps leaving humans more vulnerable to carcinogen-induced damage. We report here that IL-6 appears to repress GSTP1 expression in human Hep3B hepatocellular carcinoma cells, via augmenting C/EBPβ trans-repression of the GSTP1 promoter. In our analyses, we found that IL-6 treatment induced binding of C/EBPβ to a cis-regulatory sequence located at −326 nt to −317 nt 5′ of the transcription start site in the GSTP1 promoter, and that siRNA-catalyzed decreases in C/EBPβ levels prevented IL-6-associated GSTP1 promoter repression.; During the pathogenesis of human hepatocellular carcinoma (HCC), the CpG island encompassing the π-class glutathione S-transferase gene (GSTPI) becomes hypermethylated. We report here that inhibition of transcription from hypermethylated GSTP1 promoters in Hep3B HCC cells, which fail to express GSTP1 mRNA or GSTP1 polypeptides, appears to be mediated MBD2. Bisulfite sequencing was used to map the methylation patterns of the GSTP1 promoter region in GSTP1 expressing and nonexpressing clones. Chromatin immunoprecipitation experiments revealed the presence of MBD2, but not Sp1, at the GSTP1 promoter in Hep3B cells. SssI-catalyzed methylation of GSTP1 promoter sequences resulted in diminished luciferase reporter activity in Hep3B cells. When hypermethylated GSTP1 promoter sequences were transfected into Hep3B cells that had been treated with siRNA targeting MBD2 mRNA, no repression of luciferase reporter expression was evident.; Additionally, we undertook bisulfite genomic sequencing of the human GSTP1 CpG island in a variety of human liver diseases. These results revealed that the GSTP1 promoter typically accumulates hypermethylation in HCC. However, during alcohol cirrhosis and hepatitis infection in the absence of HCC, there is no aberrant hypermethylation of the GSTP1 promoter. |
