Supplemental Fig S8. Hypermethylation of the Igf1r aligns with sites of histone methylation. (A) The UCSC Genome Browser was used to align the Igf1r with other epigenetic modifications. The red bar indicates the region of differential DNA methylation identified in the SureSelectXT Methyl-Seq Assay. Black bars represent sites of histone methylation, the intensity corresponds to the degree of methylation. (B) Igf1r bisulfite sequencing data are depicted. Each animal is numbered and each horizontal line represents DNA from a separate clone from that animal. The percent methylation of each animal is listed under each CpG site. Open circles = unmethylated, and closed circles = methylated. The lower panel represents a combined result from all clones in all animals.
ARTICLE ABSTRACT
The most effective natural prevention against breast cancer is an early first full-term pregnancy. Understanding how the protective effect is elicited will inform the development of new prevention strategies. To better understand the role of epigenetics in long-term protection, we investigated parity-induced DNA methylation in the mammary gland. FVB mice were bred or remained nulliparous and mammary glands harvested immediately after involution (early) or 6.5 months following involution (late), allowing identification of both transient and persistent changes. Targeted DNA methylation (109 Mb of Ensemble regulatory features) analysis was performed using the SureSelectXT Mouse Methyl-seq assay and massively parallel sequencing. Two hundred sixty-nine genes were hypermethylated and 128 hypomethylated persistently at both the early and late time points. Pathway analysis of the persistently differentially methylated genes revealed Igf1r to be central to one of the top identified signaling networks, and Igf1r itself was one of the most significantly hypermethylated genes. Hypermethylation of Igf1r in the parous mammary gland was associated with a reduction of Igf1r mRNA expression. These data 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. This supports the approach of lowering IGF action for prevention of breast cancer, a concept that is currently being tested clinically. Cancer Prev Res; 8(10); 1000–9. ©2015 AACR.
