Abstract 835: Elevated in utero estrogenic environment may increase later breast cancer risk by down-regulating miRNAs

Abstract

Abstract Objectives: High maternal estrogen levels during pregnancy increase a female offspring's breast cancer risk in women and in animal models. This increase is proposed to be mediated by epigenetic changes that involve DNA methylation. Dynamic changes in miRNA expression during fetal development also play a key role in setting gene transcription patterns that persist through the life-time. In this study, we investigated whether in utero exposure to excess estradiol (E2) causes persistent changes in the expression of miRNAs and their target genes. Methods: Pregnant Sprague Dawley rats were fed AIN93G diet supplemented with 0.1 ppm ethinyl estradiol between gestation days 13 and 20. Offspring's mammary glands were obtained on postnatal day 50, and miRNAs were measured using applied Biosystems TaqManR Array Rodent MicroRNA and mRNAs using RG_U34A Affymetrix platform. Data generated in the two arrays were analyzed by an integrated approach which uses a sequence-based TargetScan method to predict miRNA targets and then correlates these targets with mRNA data to identify targets specific to in utero E2 exposure. Results: Maternal E2 exposure during pregnancy increases carcinogen-induced mammary tumorigenesis in the offspring (final tumor incidence in controls: 56%, in E2 offspring: 82%, p<0.05). Fifteen miRNAs are significantly down-regulated in the mammary glands of adult rats exposed to E2 in utero, compared to the controls. Many of these are known to be down-regulated by E2 in MCF-7 human breast cancer cells including miR-21, miR-23ab, miR-27ab, and miR-200c. Some of these miRNAs and others that are down-regulated in the mammary glands of in utero E2 exposed rats (let-7, miR-26ab, miR-181, and miR-203), in turn, suppress the expression of estradiol-regulated genes, as defined by Cicatiello et al., 2010. We also found that of the known ER-α activated genes, more than 10% are significantly up-regulated in the E2 group. These genes included BCL2L1, CYP1B1, and IGF1R. Conclusions: Our findings indicate that maternal exposure to excess E2 during pregnancy may cause a persistent up-regulation of estrogen-regulated genes by suppressing miRNAs that target these genes. Of note is that some of the miRNAs found to be down-regulated in the E2 group suppress genes known to be involved in DNA methylation. For example, miR-21 targets DNMT1; our study indicates that mammary glands of rats exposed to excess E2 in utero express significantly elevated DNMT1 levels, compared to the controls. Thus, changes in miRNAs may also be involved in inducing DNA methylation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 835. doi:10.1158/1538-7445.AM2011-835