Blockade of cMYC oncogenic function by pregnancy-induced alterations and remodeling of the mammary gland

Abstract/Project Summary The goal of this proposal is to understand how transitions through pregnancy influence the molecular and cellular state of mammary epithelial cells and oncogenesis. Numerous epidemiological studies have found that pregnancy alters the risk of breast cancer. These studies have shown consistently that a full-term pregnancy

prior to the age of 25 is associated with a one-third decrease in the life-time incidence of breast cancer. While a protective effect of pregnancy has been validated in rodent models of cancer, the underlying molecular basis for this effect remains unclear. We have found that pregnancy leads to persistent changes in the epigenome and enhancer landscape of MECs.

Using an inducible c-MYC mouse model, we also find that oncogenesis and the transcriptional output downstream of this oncogene are reduced in post-pregnancy MECs. In this proposal we will investigate the molecular basis underlying these robust phenotypes. We will use epigenomics, ex vivo, in vivo and biochemical

methods to define how the transcriptional function of c-MYC is modulated by pregnancy. We hypothesize that c- MYC interactions with cofactors and with specific cis-regulatory elements are altered in this system. We will also study how specific chromatin regulators contribute to pregnancy-mediated epigenomic rewiring.

These efforts will build upon our recent data suggesting that EZH2 supports the post-pregnancy epigenome in wild-type mice. Collectively, this research will provide fundamental insights into the cell biology of the mammary gland and carry the potential for discoveries that could be harnessed to develop preventative treatments that

modulate breast cancer risk in humans.