Date of Graduation

5-2014

Document Type

Dissertation (PhD)

Program Affiliation

Cancer Biology

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Dihua Yu, MD, PhD

Committee Member

Varsha Gandhi, PhD

Committee Member

Pierre McCrea, PhD

Committee Member

Mien-Chie Hung, PhD

Committee Member

Hui-Kuan Lin, PhD

Committee Member

Francisco Esteva, MD

Abstract

Signaling pathways that play critical roles in organ development are often aberrantly regulated during cancer initiation and progression. 14-3-3z is overexpressed in more than 40% of breast cancers and is associated with poor patient prognosis. Therefore, the function of 14-3-3z in cancer and normal mammary gland development was investigated utilizing multiple in vivo and in vitro approaches. 14-3-3z is a chaperone protein that interacts with a multitude of oncogenes and tumor suppressor genes, thereby functioning as a critical node in multiple oncogenic signaling networks. Mammary gland-specific 14-3-3z transgenic mouse models showed that 14-3-3z overexpression was sufficient to induce mammary tumorigenesis. 14-3-3z-overexpressing tumors exhibited inhibition of apoptosis and increased proliferation. Mechanistically, 14-3-3z decreased p53 expression and retained Akt-phosphorylated FKHRL in the cytosol, inhibiting transcription of pro-apoptotic genes. Additionally, 14-3-3z enhanced MAPK/c-Jun signaling leading to increased miR-221 transcription, which inhibited p27 translation, resulting in increased cell proliferation. Importantly, this 14-3-3z/miR-221/p27/proliferation axis also functions in patients' breast tumors and associates with high-grade cancers. While 14-3-3z has been identified as a crucial player in tumorigenesis, its function in normal mammary gland development remains unknown. Using 14-3-3z conventional knockout mice, we found that loss of 14-3-3z resulted in a significant delay in mammary gland ductal elongation, and decreased branch points, terminal end buds, and proliferation compared to wildtype littermates. In mammary fat pad transplantation assays, 14-3-3z-knockout (14-3-3z-/-) mammary epithelial cells (MECs) had reduced ductal outgrowth and a competitive growth disadvantage compared to wildtype (14-3-3z+/+) MECs. Interestingly, the developmental defects in 14-3-3z-/- mice correlated with a reduction in mammary stem cell (MaSC)-enriched basal population and an increase in the luminal population, indicative of decreased MaSC-self-renewal and increased luminal differentiation. Furthermore, 14-3-3z-/- mammary outgrowths presented aberrant ductal structure and deficiencies in alveogenesis and milk production whereas 14-3-3z+/+ outgrowths retained proper ductal structure and functionality. Together, our findings show that 14-3-3z overexpression plays a causal role in mammary tumorigenesis and progression through deregulation of an integrative signaling network and establishes 14-3-3z as an important player in the homeostatic growth and function of the mammary gland.

Keywords

Breast cancer, mammary development, 14-3-3zeta, ywhaz, miR-221, stem cells, cell fate

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