Abstract
HER2/neu (HER2) and cyclin E are important prognostic indicators in breast cancer. As both are involved in cell cycle regulation we analyzed whether there was a direct interaction between the two. HER2 and cyclin E expression levels were determined in 395 breast cancer patients. Patients with HER2-overexpression and high levels of cyclin E had decreased 5-year disease-specific survival compared with low levels of cyclin E (14% versus 89%, P0.0001). In vitro studies were performed in which HER2-mediated activity in HER2-overexpressing breast cancer cell lines was downregulated by transfection with HER2 small interfering RNA or treatment with trastuzumab. Cyclin E expression levels were determined by western blot analysis, and functional effects analyzed using kinase assays, MTT assays were used to assess cell viability as a marker of proliferation and fluorescence-activated cell sorting analysis was used to determine cell cycle profiles. Decreased HER2-mediated signaling resulted in decreased expression of cyclin E, particularly the low molecular weight (LMW) isoforms. Decreased HER2 and LMW cyclin E expression had functional consequences, including decreased cyclin E-associated kinase activity and decreased proliferation, because of increased apoptosis and an increased accumulation of cells in the G1 phase. In vivo studies performed in a HER2-overexpressing breast cancer xenograft model confirmed the effects of trastuzumab on cyclin E expression. Given the relationship between HER2 and cyclin E, in vitro clonogenic assays were performed to assess combination therapy targeting both proteins. Isobologram analysis showed a synergistic interaction between the two agents (trastuzumab targeting HER2 and roscovitine targeting cyclin E). Taken together, these studies show that HER2-mediated signaling effects LMW cyclin E expression, which in turn deregulates the cell cycle. LMW cyclin E has prognostic and predictive roles in HER2-overexpressing breast cancer, warranting further study of its potential as a therapeutic target.
Original language | English (US) |
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Pages (from-to) | 3896-3907 |
Number of pages | 12 |
Journal | Oncogene |
Volume | 29 |
Issue number | 27 |
DOIs | |
State | Published - Jul 8 2010 |
Keywords
- HER2/neu
- breast cancer
- cell cycle regulation
- cyclin E
ASJC Scopus subject areas
- Molecular Biology
- Genetics
- Cancer Research