Recent epidemiology studies have linked the accumulation of organochlorine pesticide (OCP) residues and polychlorobiphenyls (PCBs) in human breast fat with a significantly increased risk of breast cancer. Other studies indicate an increased risk with smoking, possibly due to polycyclic aromatic hydrocarbons (PAH), which also readily partition into breast fat. This laboratory has recently cloned a novel type of cytochrome P450 (CYP1B1) which is particularly active in converting PAH to the most highly carcinogenic bay region dihydrodiol epoxides. In human breast carcinoma cells (MCF-7), CYP1B1 appears also to convert 3I3-estradiol (E2) to the potentially carcinogenic 3,4-catechol estrogen. The related CYP1A1 (41% identical) is also expressed in human breast cells and is likewise active in PAH metabolism. Synthesis of both CYPlA1 and CYP1B1 is stimulated by 2,3,7,8-tetrachlorodibenzodioxin (TCDD), PCBs, and PAHs, each acting through the Ah-receptor. In MCF-7 cells, this induction is dependent on stimulation of estrogen receptors. We have recently shown that CYP1A1 and CYP1B1 in cultured rat mammary cells are very selectively expressed in, respectively, epithelia and stromal fibroblasts while also exhibiting similar steroid regulation (induction by E2, suppression by progesterone, cortisol). This research will develop methods (specific PCR amplification and in situ hybridization) to measure expression of CYPlA1 and CYP1B1 mRNA in human breast cells previously generated from many individual donors and stored and documented by the University of Wisconsin Clinical Cancer Center. The subsequent research will test the hypothesis that OCPs, particularly the estrogenic DDE, and PCBs will enhance the expression of CYP1A1 and CYP1B1 in human breast cells and that this regulation will be both hormonally dependent and cell-type selective. Epithelial cells and fibroblasts from individual donors will be assessed for the effects of age and breast cancer risk. Future breast tissue collections will provide breast fat OCP and PCB measurements as an additional parameter. Cell preparations will also be characterized and cell-sorted by use of fluorescent cell surface markers. We will test the hypothesis that P450- mediated chemical stress to breast fibroblasts stimulates release of growth factors and matix proteins that will potentiate the growth of basally or chemically initiated epithelial cells. We expect these experiments with this unique collection of human breast cells to provide mechanistic insight into the potential for breast cancer enhancement by environmental OCPs and PCBs.
