Regulation of transcription of the glutathione S-transferase P1 gene by methylation of the minimal promoter in human leukemia cells

To study the relationship between methylation and the transcriptional activ ity of the minimal promoter of the glutathione S-transferase GSTP1 gene enc oding glutathione S-transferase P1-1, GSTP1 mRNA levels as well as basal pr omoter activity were compared in human leukemia cell lines. The K562 erythr oleukemia cell line presented a strong GSTP1 promoter activity, as measured in transient transfection assays using a luciferase reporter plasmid, and correlated with a high mRNA whereas in Raji cells no mRNA was expressed, in order to establish a relationship between the expression and the methylati on status, we used in vitro bisulfite sequencing which indicated that both methylated and unmethylated GSTP1 promoter alleles coexisted in K562 cells, whereas Raji lymphoma cells showed a nearly uniform hypermethylation of th e promoter region. To determine the impact of methylation, we used in vitro SssI methylation of the minimal GSTP1 promoter, which led to the silencing of the promoter activity in transient transfection assays in expressing K5 62 as well as in non-expressing Raji cells. These data are in good agreemen t with previously obtained results and indicate that methylation of CpG sit es of the basal promoter is an essential mechanism in the control of GSTP1 gene expression in human leukemia. (C) 2001 Elsevier Science Inc. All right s reserved.