Abstract 2294: Pregnancy changes the DNA methylation profile of the breast in postmenopausal women

Abstract

Abstract Recently, we have described that the breast of parous postmenopausal women exhibits a specific gene expression profile induced by full term pregnancy (FTP) [Belitskaya-Levy, I. et al. 2011 and Peri, S. et al. 2012], which is centered on chromatin remodeling [Russo, J. 2012]. In order to better understand the molecular mechanism of gene regulation induced by FTP, we have investigated the DNA methylation profile in breast core needle biopsies of five nulliparous (NP) and five parous (P) postmenopausal women between the ages of 50 and 69. DNA was extracted from core needle biopsies and highly methylated fragments of the DNA were separated from the un-methylated DNA using MBD-Capture. The hypermethylated DNA was then sequenced using the Illumina system. Image analysis and base calling were performed with the standard Illumina pipeline, and the reads were aligned to human reference genome (hg18). Differentially methylated regions (DMR) were identified by comparing the differences of averaged methylation values between P and NP samples using Student's t-test (P<0.01). 583 genes were differently methylated between P and NP, of which, 455 genes were hypermethylated in the P breast and 128 genes were hypermethylated in the NP. Additional visual analyses of the sequencing results were performed in these 583 genes using Integrative Genomics Viewer (IGV), of which, 53 genes with DMRs were identified. Analysis and research into the functions of these genes identified seven genes (DACT1, PPP2CA, GSK3B, ROBO1, INPP4B, IL6ST, FZD1) that have been described to interact with each other in either the Wnt signaling pathway or its controlling PI3K/AKT/mTOR pathways. The evaluation of these interactions suggests that beta-catenin, a downstream gene of the Wnt signaling pathway, is being inhibited in the P women. Wnt signaling plays different roles during the stages of the mammary gland development, and it is suggested that lowered beta-catenin expression is essential for proper mammary involution. This observed molecular machinery, leading to a decrease in beta-catenin production and accumulation, may be a leftover effect from mammary involution, last process that the parous mammary gland undergone and it may be, at least partially, responsible for their decreased risk of cancer. The pathways identified in this specific population are of the great importance and could represent a safeguard mechanism mediating the protection of the breast conferred by full term pregnancy. (The sample collection was supported by Avon Foundation for Women Breast Cancer Research Program grant 02-2010-117 and the methylation studies by NIH core grant CA06927 to Fox Chase Cancer Center). Citation Format: Julia Santucci-Pereira, Colleen O'Malley, Ricardo López de Cicco, Nameer B. Kirma, Tim H. Huang, Joseph Liu, Eric A. Ross, Michael Slifker, Suraj Peri, Irma H. Russo, Pal Bordas, Per Lenner, Göran Hallmans, Paolo Toniolo, Jose Russo. Pregnancy changes the DNA methylation profile of the breast in postmenopausal women. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2294. doi:10.1158/1538-7445.AM2014-2294