I105V polymorphism and promoter methylation of the GSTP1 gene in prostate adenocarcinoma

The GSTP1 gene encodes for an enzyme, glutathione S-transferase π(GSTπ), involved in detoxification of carcinogens. An amino acid substitution (I105V) in GSTP1 produces a variant enzyme with lower activity and less capability of effective detoxification. This variant GSTP*B allele has been associated with a propensity to develop several neoplasms. Because GSTP1 promoter hypermethylation and inactivation of GSTπ expression is a frequent alteration in prostate carcinoma, we hypothesized that this somatic epigenetic modification could obviate any reduced enzyme activity caused by the germ-line polymorphism. We tested for the GSTP1 genotype in a population of prostate cancer patients, and in a control group composed of patients with benign prostatic hyperplasia (BPH) and healthy blood donors. Tissue samples from the 105 prostate cancer cases (105 adenocarcinomas and 34 prostatic intraepithelial neoplasia lesions), and from 43 BPH patients were tested for GSTP1 hypermethylation by methylation-specific PCR. GSTπ protein expression was assessed by immunohistochemistry. No significant effect on prostate cancer risk was detectable for GSTP1 genotype compared with the control population (odds ratio, 1.02; 95% confidence interval, 0.59-1.75). Moreover, no association was found between this genotype and tumor or BPH methylation status. Patients with unmethylated carcinomas did not disclose significant differences in genotypic distribution compared with the control population. In adenocarcinoma, a strong association (P < 0.00001) between GSTP1 promoter hypermethylation and loss of GSTπ expression was observed; however, this trend was not retained in prostatic intraepithelial neoplasia or BPH lesions. Although the GSTP1 polymorphism is not associated with altered susceptibility to prostate cancer, somatic promoter hypermethylation is an effective, but not the only, cause of decreased GSTπ function.