Investigating Mammary Ductal Stromal Interactions in the Acquisition of Tumorigenic Phenotypes

Tumor progression is an intricate process that requires manipulation and modification of the evolving tumor microenvironment. In breast cancer, disease most frequently develops in the mammary duct and progression occurs as the tumor breaks through the myoepithelium and basement layers, invading into the breast tissue. Invading cells can extravasate, leading to metastasis throughout the body. Metastatic breast cancer is the deadliest form of breast cancer, pointing to a need for intervention in this metastatic cascade as early as possible. We have used several model systems to examine the molecular mechanisms contributing to the acquisition of invasive capacity during early stages of tumorigenesis. In the context of pre-invasive ductal carcinoma in situ (DCIS), we found that DCIS cells rely on ARF6 activity to facilitate invasive activity. Additionally, through use of CRISPR/Cas9 mediated knockdown, we observe that loss of ARF6 results in mitotic catastrophes affecting protein localization, dysregulated midbody prevalence and proper separation of the daughter cells. As a result, DCIS cells lacking ARF6 proliferate at a slower rate than wild type DCIS cells. Furthermore, we examined the effect of the evolving microenvironment on the ability of epithelium to become invasive. We used a unique stromal cell population, dubbed PZP cells for their expression of PROCR, ZEB1 and PDGFa, that is enriched in normal healthy tissue of patients of African Ancestry. We found that PZP cells promote tumorigenesis through a combination of AKT activation and extracellular (ECM) matrix remodeling, acting as leader cells to allow epithelial cells to invade as follower cells. Additionally PZP cells contribute to other tumorigenic phenotypes including anchorage independent growth. Finally, in preliminary studies into additional stromal effects, we found that hypoxia influences affects mammary ductal epithelium behavior and induces activation of key signaling molecules. Solid tumors typically develop hypoxic cores that contribute to disease progression. We found that in hypoxic conditions, DCIS acini become smaller and abundance of pERK and CD44 increase. Together these findings identify key molecular mechanisms regulating the acquisition of invasive phenotypes during early stages of tumorigenesis and contribute to the understanding of biological contributors to the disparity experienced by patients of African ancestry.