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Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Molecular and Cellular Biology
Year Degree Awarded
Month Degree Awarded
Cancer Biology | Environmental Health | Immunology and Infectious Disease
The vast majority of breast cancers, ~70%, are not directly related to an inherited genetic mutation. Environmental factors play a dominant role in the etiology of most breast cancers. There is a subset of chemicals that are able to affect the homeostasis of hormones called endocrine disrupting chemicals (EDCs). Many of these chemicals are pervasive and persistent making the chances for lifetime exposure more prevalent. While many of these chemicals have been deemed safe, a subset of them have come under review to reassess their safety. As estrogen is critical for breast development and can act as a mitogen in estrogen receptor (ER) positive cancers which account for 70% of breast cancer cases, these chemicals are prime target of study in the progression of breast cancer.
There are several times in a woman’s life when hormonal surges are noted, including puberty, pregnancy, and menopause. These periods are called “windows of susceptibility” because the normal “brakes” are released to allow for growth, migration, and differentiation. Exposure to EDCs during these critical windows can alter or induce both the development and the progression of breast cancer. In addition to understanding the general effects of EDC exposures on cancer development, this exposure provides a unique opportunity to interrogate the interindividual variation among women, as not all EDC exposures lead to the development of cancers.
In this thesis work, we first interrogated the interindividual variation among women upon exposure to a known aryl hydrocarbon receptor agonist, PCB 126. This study aimed to investigate the impact of 3nM PCB 126 on gene expression in a panel of genetically diverse benign human breast epithelial cell (HBEC) cultures and patient derived breast tissues. RNAseq was used to examine the impact of exposure to 3nM PCB126 on gene expression across benign epithelial cells from different women. RNAseq analysis of HBEC cultures revealed a signature of 144 genes significantly altered by 3nM PCB 126 treatment. Confirmation of 8 gene targets using a panel of 12 HBEC cultures and commercially available breast cell lines demonstrated that, while the induction of canonical downstream target gene, CYP1A1, was consistent across our primary HBECs, other genes exhibited significant variability across individuals. The dependence on the activity of the aryl hydrocarbon receptor on the gene expression of the targets was confirmed using receptor inhibitors. PCB 126 could induce significant and consistent changes in gene expression associated with xenobiotic metabolism. Benign human breast tissue explant cultures were used to confirm whether PCB 126 impacted gene expression of targets in a more physiologically relevant and complex cellular system. This study demonstrated significant interindividual variation on the impact of PCB on gene expression. While the canonical genes were significantly changed other pathways (i.e. inflammation) varied widely across epithelial cells and tissues from different women. Although the induction of most genes was reliant on the AhR, significant variability was noted between genes and individuals. These data suggest that there is a bifurcation of the pathway following AhR activation that contributes to the variation in interindividual responses.
Next, we aimed to test a common EDC that is found in sunscreen known as benzophenone-3 (BP3). It is a potent UV protectant which is quickly absorbed through the skin. While it has been approved by the FDA, there is renewed interest in the safety of BP3. The focus of this study was to examine the impact that BP3 has on triple negative breast cancer (TNBC) through alterations to cells in the immune microenvironment. Our studies revealed that in the lung tumor microenvironment, exposure to BP3 not only increased the number of metastases, but also the total area of tumor coverage. We also found that BP3 caused alterations in immune populations (particularly T cells) in a tissue-dependent manner. Our data suggest that BP3 does not directly affect the proliferation of TNBC, but does increase extravasation or seeding of TNBC-derived tumors suggesting alterations of the microenvironment that contribute to the progression.
Lastly, we began the investigation into a mixture of polybrominated diphenyl ethers (PBDEs). While the production of these chemicals has been halted for decades, they are highly resistant to degradation and there are high levels of soil and air pollution. The focus of this study was to understand the impact that PBDEs have on TNBC breast cancer development during the pubertal time point. Previous works showed that during the menopausal window of susceptibility there is an increase in the trafficking of proinflammatory immune cells which impact tumor development. Our study demonstrated that exposure to these PBDE congeners in chow from weaning until the end of the experiment resulted in a significant increase in the orthotopic growth of the 4T1 TNBCs. While the lung metastases did not exhibit significant differences in size or seeding there were some modest changes to the immune landscape in lung tumor metastases, particularly in the T cell populations.
Morin, Stephanie, "Exposure to Endocrine Disrupting Chemicals and the Effects on Inflammation and Mammary Tumor Progression" (2022). Doctoral Dissertations. 2695.
Available for download on Friday, September 01, 2023