Date on Master's Thesis/Doctoral Dissertation

12-2015

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biochemistry and Molecular Biology

Degree Program

Biochemistry and Molecular Biology, PhD

Committee Chair

Clark, Geoffrey

Committee Co-Chair (if applicable)

Samuelson, David

Committee Member

Dr. David Samuelson

Committee Member

Powell, David

Committee Member

Prough, Russell

Committee Member

Samuelson, David

Committee Member

Kalbfleisch, Theodore

Author's Keywords

Ras; NORE1A; BRCA1; breast cancer

Abstract

Ras proteins function as molecular signaling switches that can stimulate multiple mitogenic pathways in response to extracellular signaling. Oncogenic activation of Ras by structural mutation is a highly transforming event in ~1/3 of human cancers. However, aberrant Ras activation can also promote oncogene-induced senescence. This Ras-induced irreversible growth arrest is a physiological process that acts as a barrier to malignancy. The mechanisms by which Ras drives senescence and how this process is bypassed during Ras-driven transformation remains poorly understood.

Although mutations in the RAS gene are extremely rare in human breast cancer, the Ras signaling pathway is constitutively activated in roughly half of all primary breast tumors. This is largely due to aberrant activation of upstream regulators of Ras, like the EGFR family member Her2 and inactivation of negative Ras regulators, such as NF1.

NORE1A (RASSF5) is a direct Ras effector that acts as a tumor suppressor by promoting apoptosis and senescence. Expression of NORE1A is frequently lost in primary breast tumors and breast cancer cell lines, though its mechanism of action in breast cancer pathogenesis remains unclear.

BRCA1 is a tumor suppressor that plays a key role in DNA DSB repair. Loss of BRCA1 is associated with hereditary breast and ovarian cancer, and is also thought to play a role in sporadic breast cancer. Recently, BRCA1 was shown to play a role in both Her2 and Ras senescence, but the mechanism underlying the communication between Her2/Ras and BRCA1 was not identified.

I have discovered that NORE1A forms an endogenous, Her2/Ras-regulated complex with BRCA1. I show that dual suppression of NORE1A and BRCA1 has a synergistic effect on transformation. Furthermore, I show that NORE1A loss suppresses the BRCA1-mediated senescence effect. Finally, I show that NORE1A and BRCA1 synergize to modulate DNA repair. Thus, I identify a novel tumor suppressor complex that connects Her2/Ras senescence signaling to BRCA1 in breast cancer.

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