Date of Award

5-2007

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry and Molecular Biology

Advisor

Lucy Liaw

Second Committee Member

Jeong Yoon

Third Committee Member

Joseph Verdi

Abstract

Notch signaling is associated with activation of either oncogenic or tumor suppressor activities. The human mammary adenocarcinoma cell line, MDA-MB-231, was characterized in vitro and in xenografts in vivo to test the hypothesis that activation of Notch signaling regulates mammary tumor phenotype. Notch 1, Notch2, and Notch4 signaling was compared by stable expression of their constitutively active intracellular domains (ICD). Notch4 activation led to enhanced tumorigenicity, in addition to increased cell proliferation and survival in vitro, whereas the activation of Notch 1 or Notch2 decreased cell proliferation and survival, in which Notch2 increased apoptosis. Stably transfected cell lines were additionally studied in vivo as xenografts. Overexpression of Notch4ICD promoted tumor growth which resulted in a three-fold increase in tumor volume than control. Conversely, Notch IICD or Notch2ICD led to decreased tumor penetrance and significantly smaller, necrotic tumors. Analysis of cell proliferation showed a positive correlation to tumor size. Notch4ICD tumors showed an increase in organized vasculature. Control tumors and Notch 1ICD tumors, in contrast, showed significant necrosis, and had fewer vessels. Although Notch2ICD tumors were small and showed low proliferation, they were highly vascularized, comparable to Notch4ICD tumors. The molecular profile of the Notch4ICD tumors showed specific induction of VEGF and HGF in the tumors and host plasma, suggesting a differential regulation of angiogenic cytokines. The stark contrast between distinct Notch receptors suggests potential antagonistic interactions between Notchl/Notch2 and Notch4 in mammary tumorigenesis. Further, the combination of cell proliferation and vascularization contribute differentially to overall tumor phenotype.

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