Cytosine methylation represses glutathione S-transferase P1 (GSTP1) gene expression in human prostate cancer cells

Methylation of the glutathione S-transferase pi (GSTP1) gene has been descr ibed as a highly specific and sensitive biomarker for prostate cancer. Howe ver, at present, it is not known whether methylation represses GSTP1 gene e xpression in human prostate canter, We found the GSTP1 gene promoter to be completely methylated in the LNCaP prostate cancer cell line, where this ge ne is transcriptionally inactive. In contrast, Du145 and PC3 prostate cance r cells express the GSTP1 gene and exhibit methylated and unmethylated GSTP 1 alleles, In a transient transfection assay using LNCaP cells, methylation of the GSTP1 promoter-driven luciferase reporter vector (GSTP1-pGL3) resul ted in a > 20-fold inhibition of transcription, and this repression was not relieved by the presence of a histone deacetylase inhibitor, trichostatin A (TSA). Treatment of LNCaP cells with a DNA methyltransferase inhibitor, 5 -Aza-2 ' -deoxycytidine, resulted in demethylation and activation of the GS TP1 gene. In contrast, TSA treatment failed to demethylate or activate the GSTP1 gene. Fully methylated but not unmethylated GSTP1 promoter fragment w as shown to bind to a complex similar to methyl cytosine-binding protein co mplex 1 that contains methyl-CpG-binding domain 2 protein (MBD2) in electro phoretic mobility shift assays using LNCaP cell nuclear extracts. These dat a demonstrate that cytosine methylation can repress GSTP1 gene expression i n LNCaP prostate canter cells and that this effect is possibly mediated by a methyl cytosine-binding protein complex 1-like complex. Furthermore, thes e data also support the notion of the dominance of methylation over TSA-sen sitive histone deacetylation in silencing genes with a high CpG density in the promoter region.