Lipid-initiated epigenetic reprogramming of the breast to a neural phenotype

The known determinants of risk for estrogen receptor (ER)-negative breast cancer are genetic or systemic/behavioral factors. In contrast, few if any local factors in the breast environment serve to identify women at risk for ER negative tumors. Local in-breast factors are of great interest however, since they may be more specifically targetable for breast cancer prevention than systemic factors. In this innovative submission, we propose that the expression of neural genes, a recently identified “Hallmark of Cancer”, results from epigenetic reprogramming consequent to lipid-induced altered metabolic flux. Studies of metachronous breast cancers that develop in the opposite breast show a similarity to the ER status of the index primary. Therefore, we employed the contralateral unaffected breast (CUB) of women undergoing surgical therapy for newly diagnosed unilateral breast cancer as a model to discover potential markers of ERrisk. In a previous study, we identified a lipid metabolism (LiMe) gene signature, which was enriched in the CUBs of women with ER- breast cancer. In order discover mechanisms by which lipid metabolism pathways would aid ER- breast cancer development, we established an in vitro model in which the ER and progesterone receptor (PR) negative cell lines MCF10A/12A and breast microstructures are exposed to octanoic acid (OA), a medium chain eight-carbon fatty acid. Using this model system, we observed dynamic and profound changes in gene expression, accompanied by changes in chromatin packing density, chromatin accessibility and histone methylation. Significant increase in metabolic flux was observed in 38 reactions, among them those of the serine, onecarbon, glycine (SOG) pathway and the methionine cycle with a consequent increase in S-adenosylmethionine (SAM) concentration. An intriguing and unexpected finding was expression of genes involved in nervous system development, which we hypothesize results from SAM driven histone methylation. We propose to pursue these provocative results as follows. Aim 1 explores whether the OA-mediated increase in the expression of specific neural genes is also observed at the protein level. Based upon gene expression, a specific subset of basal cells (BSL1) are hypothesized to be those undergoing the epithelial to neural flip. BSL1 will be isolated from breast microstructures, exposed to OA and assayed for neurite outgrowth. Aim 2’s goal is to determine which other histone methylations are responsible for the increased expression of genes associated with neurons and decreased expression of those associated with epithelial cells. Aim 3 is constructed to determine whether specific SNPs associated with ER-breast cancer produce a microenvironment in vivo that mirrors the OA rich experimental environment. These investigations have the potential to reveal a set of novel metabolic-fostered alterations that may be utilized as targets for breast cancer prevention.