Abstract P5-11-05: Pregnancy-induced epigenetic changes in the insulin-like growth factor signaling pathway
Authors: Katz Tiffany A , Liao Serena G , Pathiraja Thushangi , Dearth Robert K , Tseng George C , Oesterreich Steffi , Lee Adrian V 
Published: May 2015

Abstract
Prevention will prove to be the single most effective way of eradicating breast cancer. Currently, the most effective natural breast cancer prevention is an early first full term pregnancy. While it is not feasible to use pregnancy to protect women from breast cancer, understanding how the protective effect is elicited will inform the development of new prevention strategies. Women who were pregnant in their twenties are protected thirty to forty years later creating a complicated mechanism to tease out experimentally. In order to understand the long-term protection we have investigated epigenetics, specifically DNA methylation, which is known to be stable over long periods of time. A cohort (Parous) of female FVB mice were bred, gave birth, and pups were weaned. A control group (Nulliparpous) never saw male mice. Mammary glands were harvested immediately or 6 months after involution. These two time points allowed us to identify changes in DNA methylation that occurred in response to pregnancy, and additionally, changes that lasted long after parturition. DNA was isolated, and genome-wide DNA methylation was assessed using bisulfite-conversion and SureSelect Methyl-Seq. Bismark v0.7.12 was used for alignment of pair-end reads, followed by the R package "methylKit" for quality control and data analysis. A mapping efficiency of 50%∼68.1% was achieved with 89,512,619 base pairs covered. CpG Pearson correlation plots and PCA analysis showed global similarity between samples. We then conducted a logistic regression to ascertain parity-induced differentially methylated regions and identified 153 and 236 persistently hypomethylated and hypermethylated genes, respectively. Among the differentially methylated genes were many signaling molecules involved in growth factor signal transduction, including insulin-like growth factor 1 and 2 receptors (IGF1R and IGF2R). It has previously been shown that circulating IGF1 levels are reduced in parous women, and similarly the growth hormone/IGF axis is altered in rodent models. Collectively, these findings suggest that the IGF pathway is regulated at multiple levels during pregnancy, and that its modification might be critical in the protective role of pregnancy. We are currently following up on these data, including protein analysis of the IGF pathway members and downstream signaling molecules in human specimens. Finally, we are expanding our analysis to additional genes and pathways epigenetically altered by pregnancy, with the ultimate goal to develop new prevention strategies.
Citation Format: Tiffany A Katz, Serena G Liao, Thushangi Pathiraja, Robert K Dearth, George C Tseng, Steffi Oesterreich, Adrian V Lee. Pregnancy-induced epigenetic changes in the insulin-like growth factor signaling pathway [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-11-05.