DNA Promoter Methylation in Breast Tumors Is Not Associated with Polymorphism in the GSTP1 Gene.

Abstract

Abstract The gluthathione S-transferases (GSTs) are a family of enzymes that play an important role in detoxification of a variety of potential carcinogenic, hydrophobic and electrophilic compounds. Glutathione-S-transferase P1 (GSTP1) is involved in thiol-mediated detoxification and breakdown of reactive oxygen species created by anticancer drug exposure. It is also an inhibitor of c-Jun N-terminal kinase 1 which is involved in stress response, apoptosis and cellular proliferation. It has been postulated that a decrease in GST enzyme activity could result in higher frequency and a specific pattern of mutations in cancer. Loss of GSTP1 expression is observed in approximately two thirds of breast cancer cases, which indicates its potential role in breast carcinogenesis. The GSTP1 gene exhibits deletion polymorphisms and homozygous deletion of the gene may result in lack of enzyme activity. The polymorphism in the GSTP1 gene results from a base substitution and leads to an amino acid change at codon 105. This amino acid resides at the substrate binding site of the enzyme and may modify the catalytic activity of the enzyme several-fold.DNA methylation is an important epigenetic modification of the genome. A specific methylation pattern has been observed in various types of cancers. Hypermethylation of the GSTP1 promoter has also been associated with gene silencing in different forms of cancer. In a previous study we have found that the GSTP1 gene was the second most frequently methylated gene in breast cancer. However, a possible relationship between the methylation status of the gene promoter and GSTP1 polymorphic variants has not been investigated.In this study we investigated the role of the different allelic variants in the methylation status of the GSTP1 gene in patients with breast cancer. A total of 48 patients with breast cancer and 32 healthy women were analyzed. The GSTP1 polymorphism was determined by PCR-RFLP. Methylation of the GSTP1 gene was evaluated by methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) using probes targeting the GSTP1 gene and metylation-sensitive enzyme digestion of the probe-DNA hybrids. The amplified products were analyzed by sequence-type capillary electrophoresis. Subsequent quantification of the methylation status was performed by comparing the relative signal peaks from the digested and undigested samples.The null allele was observed in % 56,2 of the patients and % 46.8 of the control group, respectively. No significant difference was observed between the distribution of the genotypes in the patients and the controls. The GSTP1 gene promoter was methylated in % 39.6 of the patients. However, the distribution of the genotypes and allele frequencies did not reveal any preferential methylation of a specific allele. The genotypes were not associated with increased likelihood of promoter methylation. Our data indicate that the deletion allele of the GSTP1 gene does affect the methylation status of the gene in breast cancer. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1150.