Breast cancers with overexpression or amplification of the HER2 tyrosine kinase receptor are more aggressive, resistant to chemotherapy, and associated with a worse prognosis. Currently, these breast cancers are treated with the monoclonal antibody trastuzumab (Herceptin®). Unfortunately, not all patients respond to trastuzumab drug therapy; some patients show de novo resistance, while others acquire resistance during treatment. This thesis describes our RNAi studies to identify novel regulators of the HER2 signaling pathway in breast cancer.
Three kinome-wide siRNA screens were performed on five HER2 amplified and seven HER2 non-amplified breast cancer cell lines, two normal breast cell lines, as well as two HER2-positive breast cancer cell lines with acquired trastuzumab resistance and their isogenic trastuzumab-sensitive controls. To understand the main kinase drivers of HER2 signaling, we performed a comprehensive screen that selected against growth inhibitors of the non-HER2 amplified breast cancer cell lines. This screen identified the loss of the HER2/HER3 heterodimer as the most prominent selective inhibitor of HER2-amplified breast cancers. In a trastuzumab sensitization screen on five trastuzumab-treated breast cancer cell lines, we identified several siRNA against the PI3K pathway as well as various other signaling pathways that inhibited proliferation. Finally, in a screen for acquired trastuzumab resistance, PKCη and its downstream targets were identified. Loss of PKCη resulted in a decrease in G1/S transition and upregulation of the cyclin dependent kinase inhibitor p27. Initial data suggest that PKCη promotes p27 ubiquitination and degradation.
Taken together, these studies provide novel insight into the complex signaling of HER2-positive breast cancers and the mechanisms of resistance to trastuzumab therapy. This work describes how various kinases can modulate cell proliferation, and points to possible novel drug targets for the treatment of HER2-positive breast cancers.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/35712 |
| Date | 17 July 2013 |
| Creators | Lapin, Valentina |
| Contributors | Mak, Tak Wah |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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