Date of Graduation


Document Type

Dissertation (PhD)

Program Affiliation

Cancer Biology

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Khandan Keyomarsi, Ph.D.

Committee Member

Michelle Barton, Ph.D.

Committee Member

Mong-Hong Lee, Ph.D.

Committee Member

Sendurai Mani, Ph.D.

Committee Member

Frank Marini, Ph.D.


Cyclin E is the regulatory subunit of the cyclin E/CDK2 complex that

mediates the G1-S phase transition. N-terminal cleavage of cyclin E by elastase in

breast cancer generates two low molecular weight (LMW) isoforms that exhibit both

enhanced kinase activity and resistance to p21 and p27 inhibition compared to fulllength cyclin E. Clinically, approximately 27% of breast cancer patients overexpress

LMW-E and associate with poor survival. Therefore, we hypothesize that LMW-E

disrupts normal mammary acinar morphogenesis and serves as the initial route into

breast tumor development. We first demonstrate that LMW-E overexpression in

non-tumorigenic hMECs is sufficient to induce tumor formation in athymic mice

significantly more than overexpression of full-length cyclin E and requires CDK2-

associated kinase activity. Further in vivo passaging of these tumors augments

LMW-E expression and tumorigenic potential. When subjected to acinar

morphogenesis in vitro, LMW-E mediates significant morphological disruption by

generating hyperproliferative and multi-acinar complexes. Proteomic analysis of

patient tissues and tumor cells with high LMW-E expression reveals that the

activation of the b-Raf-ERK1/2-mTOR pathway in concert with high LMW-E

expression predicts poor patient survival. Combination treatment using roscovitine

(CDK inhibitor) plus either rapamycin (mTOR inhibitor) or sorafenib (b-raf inhibitor)

effectively prevented aberrant acinar formation in LMW-E-expressing cells by

inducing the G1/S cell cycle arrest. In addition, the LMW-E-expressing tumor cells

exhibit phenotypes characteristic of the EMT and enhanced cellular invasiveness.

These tumor cells also enrich for cells with CSC phenotypes such as increased

CD44hi/CD24lo population, enhanced mammosphere formation, and upregulation of

ALDH expression and enzymatic activity. Furthermore, the CD44hi/CD24lo

population also shows positive correlation with LMW-E expression in both the tumor

cell line model and breast cancer patient samples (p<0.0001 & p=0.0435,

respectively). Combination treatment using doxorubicin and salinomycin

demonstrates synergistic cytotoxic effects in cells with LMW-E expression but not in

those with full-length cyclin E expression. Finally, ProtoArray microarray identifies

Hbo1 as a novel substrate of the cyclin E/CDK2 complex and its overexpression

results in enrichment for CSCs. Collectively, these data emphasize the strong

oncogenic potential of LMW-E in mammary tumorigenesis and suggest possible

therapeutic strategies to treat breast cancer patients with high LMW-E expression.


cyclin E, breast cancer, acinar morphogenesis, roscovitine, b-Raf-ERK1/2-mTOR pathway, cancer stem cells, epithelial-mesenchymal transition, salinomycin, Hbo1



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