The Role of Tumor Suppressor DEAR1 in the Acquisition of Mammary Stem/Progenitor Cell Properties

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Le, Uyen; <p>0000-0002-9900-9675</p>
tumor suppressor; breast cancer; cancer stem cells; stem cells; progenitor cells; mammosphere; EMT; triple-negative breast cancer; TRIM; cancer; genetics; Biology; Laboratory and Basic Science Research; Medicine and Health Sciences; Molecular Genetics
thesis / dissertation description
Breast cancer is the most commonly diagnosed cancer in women in America. Ductal carcinoma in situ (DCIS), one of the earliest pre-invasive forms of invasive ductal carcinoma (IDC), has a 30-50% risk of progressing to IDC. Understanding the mechanisms regulating progression from DCIS to IDC would help identify biomarkers to stratify patients at higher risk of progression or metastasis. Cumulative literature suggests the earliest phase of dissemination from the primary tumor is driven by the epithelial-mesenchymal transition (EMT) program. DEAR1 is a tumor suppressor gene which is mutated, undergoes loss of heterozygosity in breast cancer, and is downregulated in DCIS lesions and IDC. DEAR1 regulates acinar morphogenesis and cell polarity and is a negative regulator of TGF-β-driven EMT through inhibition of SMAD3. Studies have now demonstrated that induction of EMT promotes acquisition of stem/progenitor cell properties, further adding to the repertoire of cellular regulation by EMT mediators.I demonstrate that loss of DEAR1 in human mammary epithelial cells (HMECs) and DCIS cells results in a mammosphere phenotype independent of the canonical TGF-β pathway, suggesting that DEAR1 regulates stem/progenitor cell properties. DEAR1-knockdown (KD) HMEC mammospheres express high levels of stem/progenitor cell marker aldehyde dehydrogenase (ALDH1) and display a basal-like phenotype through repression of CD24 and EpCAM expression. There is significant upregulation of master EMT and stem cell regulators, including SNAI2, in DEAR1-KD HMECs and I show that DEAR1 binds to and promotes polyubiquitination of SNAI2. I reveal a novel DEAR1-SNAI2 axis that partially regulates stem/progenitor cell properties in HMECs and demonstrate a significant association between loss of DEAR1 in basal-like/triple-negative breast cancers (TNBC), early-age of onset, and risk of shorter time to metastasis in TNBC. Additionally, I identify a possible mechanism governing DEAR1 regulation in mammary epithelial cells through miRNAs miR-10b and miR-196b.Results herein demonstrate that DEAR1 promotes stem/progenitor cell properties partially through TGF-β-mediated EMT and also through SNAI2 independently of TGF-β-SMAD3 signaling. I hope to use this understanding of DEAR1 and its regulation of cell polarity, EMT, and stemness to stratify high risk patients who would benefit from more aggressive or targeted therapy.