| dc.description.abstract | Breast cancer is the most common cancer diagnosed among women in the United States. Breast cancer is subdivided into groups based on receptor status including estrogen receptor (ER) and progesterone receptor (PR) positive, human epidermal growth factor-2 positive (HER2) or triple-negative. Triple-negative breast cancer (TNBC) affects 15-20% of women diagnosed with breast cancer each year and is the most aggressive subtype. TNBC lacks the common receptors used to diagnose and treat breast cancer and subsequently, does not have any targeted therapies. Therefore, our long-term goal is to identify drivers of TNBC aggression and subsequent treatments to target those drivers. Evidence suggests that breast tumors expressing high levels of interferon stimulated genes (ISGs) are more aggressive than tumors expressing low levels of ISGs, perhaps providing a molecular explanation into the aggressive nature of TNBC. We have identified that TNBC breast cancer cell lines and patient samples overexpress a specific ISG called interferon inducible transmembrane 1 (IFITM1). Though studies in cancer biology have identified that IFITM1 can promote tumor progression, the role of IFITM1 in TNBC is unknown. IFITM1 is normally only expressed upon exposure to type I interferons such as interferon (IFN)-alpha, but can also be regulated by other pathways including NFκB. The goals of this thesis are to assess the clinical and functional relevance of IFITM1 in TNBC, to investigate the mechanism by which IFITM1 contributes to TNBC progression, and to uncover novel ways to target its expression. In this thesis we demonstrate that IFITM1 is significantly elevated in TNBC tumors as assessed by a TNBC tumor microarray and in silico analysis, and that IFITM1 is overexpressed in TNBC cell lines. Loss of function studies in SUM149, MDA-MB-157, and MDA-MB-468 TNBC cell lines reveal that IFITM1 regulates TNBC growth, migration, and invasion both in vitro and in vivo. RNA sequencing of CRISPR/Cas9 mediated IFITM1 knockout SUM149 cell lines suggest that loss of IFITM1 results in a decrease of NFκB mediated signaling and subsequently IL6 and SNAI2 expression. Mechanistically, data presented herein suggest IFITM1 functions to regulate TNBC cell growth with the help of CD81 likely through regulating integrin, NFκB, and IL6 gene expression. Additionally, we uncovered, for the first time, that IFITM1 is secreted in TNBC extracellular vesicles. Collectively, these findings suggest that IFITM1 contributes to TNBC progression, therefore, selectively targeting IFITM1 may be a novel therapeutic avenue for patients with IFITM1 positive TNBC. IFITM1 is normally only expressed upon exposure to type I interferons such as interferon alpha (IFNα). Canonical IFNα signaling activates a JAK/STAT phosphorylation cascade resulting in formation of a transcriptional complex comprised of phosphorylated (p-)STAT1, pSTAT2 and interferon regulatory factor-9 (IRF9). However, IFNα can promote gene expression in the absence of STAT phosphorylation due to chronic exposure to IFNα, or through crosstalk with other pathways including NFκB. Data presented herein show that IFITM1 is regulated in a STAT2/IRF9/p65 dependent manner. We identified that IFITM1 is regulated by autocrine IFNα in TNBC through unphosphorylated the STAT2/IRF9 complex, but also identified that IFITM1 is directly regulated by p65 and that IFNα can regulate p65 activation. Anchoring these data, a high throughput screen identified the NFκB inhibitor, parthenolide, to be cytotoxic to TNBC cells and we found it regulates IFITM1 expression both in vitro and in vivo. Lastly, loss of IFITM1 enhances parthenolide mediated apoptosis. Data presented in this thesis begin to characterize the functional role of IFITM1 and IFNα signaling in TNBC progression as a means for developing a more comprehensive understanding of TNBC biology in hopes of identifying potential alternative therapies. Here, we provide evidence to suggest that IFITM1 is both a potential therapeutic target and biomarker for a subset of TNBC. | |
