GSTP1 Promoter Haplotypes Affect DNA Methylation Levels and Promoter Activity in Breast Carcinomas

Abstract

The CpG island spanning the transcription start of the glutathione S-transferase P1 becomes methylated in a variety of human cancers including breast cancer. To study the effect of sequence variation on hypermethylation of the GSTP1 promoter, we analyzed the genetic and epigenetic variability in 90 tumors from patients with locally advanced breast cancer. High-resolution quantitative analysis revealed large variability in the DNA methylation levels. Lack of methylation was more often observed in the basal and normal-like estrogen receptor (ER)-negative tumors, and methylated GSTP1 was associated with better overall survival (P = 0.00063). Studies of the genetic variation identified 14 different haplotypes. The distribution of methylation levels of tumors homozygous for the most frequent haplotype was significantly different from other haplotype combinations (P = 0.011), the difference being more pronounced in ER-positive (P = 0.005) and progesterone receptor-positive (P = 0.008) tumors. Regression modeling identified the ER status and haplotype as the main determinants of DNA methylation variability. We identified a putative c-Myb response element (MRE) that was present in one of two minimal promoter haplotypes. In vitro analysis showed that c-Myb binds to the MRE, but binding was weakened by the two polymorphisms. Transient cotransfections in luminal-type and basal-like breast cancer cell lines confirmed cell-specific differential binding of c-Myb to the polymorphic sites, leading to a change in the expression from the GSTP1 promoter in vivo. GSTP1 expression was moderately but significantly (P = 0.01) reduced after siRNA-mediated knockdown of c-Myb. Our results indicate that haplotype structure of a promoter is important for the extent of DNA methylation. [Cancer Res 2008;68(14):5562-71]

Epigenetic regulation of microRNA expression in colorectal cancer

“…In this sense, it has been postulated that local sequence features can contribute to the susceptibility of a CpG island to become methylated or to be protected from methylation. 36 In summary, our study shows that miRNA-specific hypermethylation in CRC and histone-deacetylation could be an important molecular mechanism causing the global down-regulation of miRNAs. Considering the high frequency of miRNA hypermethylation found in CRC cancer, miRNA gene methylation could be considered as useful tumor marker.…”

Vitamin D receptor gene methylation is associated with ethnicity, tuberculosis, and TaqI polymorphism

“…Rather than studying genetic variants in isolation, the common disease genetic epigenetic (CDGE) hypothesis encourages the simultaneous analysis of both genetic and epigenetic variants (MVPs) to construct 'hepitypes' in order to increase the power of associations in epidemiological studies and minimise inconsistent associations [18,21]. Analysing both the genetic and epigenetic characteristics of a gene and their interaction in disease has recently been the focus of a number of studies [22][23][24]. Cis interactions between genetic and epigenetic variants involve the direct modulation of CpG methylation by SNPs [18] and the correlation of methylation with SNPs within 1 Mb of a CpG [24] while trans interactions involve regulation effects between CpGs and SNPs from more distant genomic regions, including regions from different chromosomes [24].…”

Epigenetic mechanisms and the relationship to childhood asthma

“…Thus, genomic variations in GST genes could determine the level of epigenetically active substances acting on CpGs in disease-associated candidate genes. Furthermore, it has been shown that transcriptional activity of GST promoters depends on genetic variants and leads to differential DNA methylation susceptibility of the respective promoter, as recently demonstrated in a study of locally advanced breast cancer [72].…”