DNA hypermethylation phenotypes and one carbon metabolism genetic variants in breast tissues from normal healthy women

Abstract

1 Hypermethylation of tumor suppressor genes promoter region may have important implications in understanding breast cancer etiology. In this study, we examined potential determinants of DNA hypermethylation in normal breast tissue, including genetic variants for genes important to one-carbon metabolism in relation to hypermethylation. We recruited 141 women without a history of breast or other cancers, who were undergoing reduction mammoplasty. These women underwent a structured interview and donated breast tissue and blood. Hypermethylation phenotypes for p16 INK4 , BRCA1, ERα and RAR-β from the normal breast tissues were determined by MSP and Pyrosequencing assays. Genetic variants of MTHFR and MTR genes were determined by TaqMan assays. Chi-square, t tests and logistic regression model were used to determine the association between promoter hypermethylation of these genes and genotypes and other characteristics of these women.
 The mean age of women was 35+/-12 years. p16 INK4 , BRCA1, ERα and RAR-β promoter hypermethylation was identified in 31%, 16% 9% and 0% of women respectively. Race was significantly associated with the methylation status (p-value=0.03). When we stratified these women by race we observed that p16 INK4 hypermethylation was associated with family history of cancer, with the variant allele of the MTR A2756G polymorphism and marginally associated with alcohol consumption (p-value=0.01; 0.02 and 0.05) only in Caucasian women. There were no significant associations for African-American women. BRCA1 hypermethylation was significantly associated with family history of cancer (p-value=0.03) for African-American women. Family history of cancer in Caucasians and family history of breast cancer for African-American women were weakly associated with BRCA1 methylation (p-value=0.09; 0.06 respectively). ERα methylation phenotype was significantly correlated with the age of both Caucasian and African-American women (p MTR 2756G were also weakly associated with ERα hypermethylation in African-American women (p-value=0.08; 0.08 and 0.09 respectively).
 The presence of hypermethylation of important tumor suppressor genes was a common finding in apparently healthy women without history of breast cancer. Several known risk factors for breast cancer were associated with increased risk of hypermethylation, as were genetic variants for MTR gene. There were important differences in these associations by race. Understanding the determinants of hypermethylation in normal breast tissues can provide insight into a potentially significant mechanism for breast carcinogenesis.
 Supported by: DOD BC022346