Defense Date


Document Type


Degree Name

Master of Science



First Advisor

Hisashi Harada


Breast cancer is the second leading cause of death amongst women ages 20 to 59. Despite advancements in cancer therapies, more research is necessary to improve the diagnoses and treatment of several types of breast cancer. Paclitaxel (Taxol) is a commonly utilized anti-cancer drug for various types of solid tumors. However, the molecular mechanism utilized by paclitaxel to induce cell death is still elusive. Previous studies in our laboratory have shown that the pro-apoptotic BCL-2 family protein, BAK (BCL-2 homologous antagonist/killer) plays an important role in paclitaxel-induced cell death. In untreated breast cancer cells, BAK is associated with the anti-apoptotic BCL-2 family protein MCL-1 (myeloid leukemia cell differentiation protein). BAK is activated with paclitaxel treatment in concert with loss of MCL-1 expression. In addition, it has been shown that the pro-apoptotic BH3-only BCL-2 family protein Noxa, specifically interacts with MCL-1 to inactivate MCL-1 function. Based on these observations, we hypothesized that modulation of Noxa/MCL-1 axis could mimic paclitaxel-induced cell death. Here, we found that down-regulation of MCL-1 induced cell death in all breast cancer cell lines that we tested, but not in a non-transformed breast epithelial cell line. In contrast, Noxa overexpression induced MCL-1 degradation and cell death in some cell lines (Noxa-sensitive), while in others Noxa overexpression neither changed MCL-1 levels nor induced cell death (Noxa-resistant). Noxa strongly interacted with MCL-1 in the Noxa-sensitive cell line, but not in the Noxa-resistant cell line. Based on these findings, the overexpression of Noxa might have two different mechanistic effects on MCL-1 levels in the breast cancer cell lines (induction of MCL-1 degradation or no effect on MCL-1). In Noxa-sensitive cells, the finding could be used as a potential therapeutic strategy for the treatment of breast cancer.


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