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Combinatorial PX-866 and Raloxifene Decrease Rb Phosphorylation, Cyclin E2 Transcription, and Proliferation of MCF-7
Gregory W Peek1, Trygve O Tollefsbol1,2,3,4,5
1Department of Biology, University of Alabama, Birmingham, Alabama.
Abstract:
As a potential means to reduce proliferation of breast cancer cells, a multiple-pathway approach with no effect on control cells was explored. The human interactome being constructed by the Center for Cancer Systems Biology will prove indispensable to understanding composite effects of multiple pathways, but its discovered protein-protein interactions require characterization. Accordingly, we explored the effects of regulators of one protein on downstream targets of the other protein. MCF-7 estrogen receptor-positive (ER+) breast cancer cells were treated with raloxifene to upregulate the TGF-β pathway and PX-866 to down-regulate the PI3K/Akt pathway. This resulted in highly significant downstream reduction of cell cycle proliferation in breast cancer cells with no significant proliferation reduction following similar treatment of noncancerous MCF10A breast epithelial cells. Reduced phosphorylation of p107 and substantial reduction of Rb phosphorylation were observed in response. The effects of reduced Rb and p107 phosphorylation were reflected in significant decline in E2F-1 transcriptional activity, which is dependent on pocket protein phosphorylation status. The reduced proliferation was related to decreased expression of cyclins, including E2F-1-regulated Cyclin E2, which was also in response to raloxifene and PX-866. All combinations of raloxifene and PX-866 produced significant or highly significant results for reduced MCF-7 cell proliferation, reduced Cyclin E2 transcription, and reduced Rb phosphorylation. These studies demonstrated that uncontrolled proliferation of ER+ breast cancer cells can be significantly reduced by combinational targeting of two relevant pathways. J. Cell. Biochem. 117: 1688-1696, 2016. © 2015 Wiley Periodicals, Inc.
Insights
Targeting the TGF-β and PI3K/Akt pathways simultaneously significantly reduces estrogen receptor-positive breast cancer cell proliferation. This dual-pathway approach effectively inhibits cancer cell growth without impacting normal cells.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Understanding complex signaling pathways is crucial for developing targeted breast cancer therapies.
- The human interactome provides a framework for analyzing the composite effects of targeting multiple pathways.
- Characterizing protein-protein interactions is essential for deciphering pathway crosstalk.
Purpose of the Study:
- To investigate the efficacy of a combined therapeutic strategy targeting the TGF-β and PI3K/Akt pathways in breast cancer.
- To evaluate the impact of this dual-pathway inhibition on cell cycle proliferation in estrogen receptor-positive (ER+) breast cancer cells.
- To assess the specificity of the treatment by comparing its effects on cancerous versus non-cancerous breast epithelial cells.
Main Methods:
- MCF-7 (ER+) breast cancer cells and MCF10A (non-cancerous) cells were treated with raloxifene (to upregulate TGF-β) and PX-866 (to down-regulate PI3K/Akt).
- Cell proliferation, phosphorylation status of key proteins (p107, Rb), E2F-1 transcriptional activity, and cyclin expression (including Cyclin E2) were analyzed.
- Statistical significance was determined for all measured outcomes.
Main Results:
- Combined treatment with raloxifene and PX-866 significantly reduced proliferation in MCF-7 cells but not in MCF10A cells.
- A substantial decrease in Rb and p107 phosphorylation was observed, leading to reduced E2F-1 transcriptional activity.
- Decreased expression of E2F-1-regulated Cyclin E2 was noted in response to the combined therapy.
Conclusions:
- Combinational targeting of the TGF-β and PI3K/Akt pathways offers a promising strategy for reducing uncontrolled proliferation of ER+ breast cancer cells.
- The observed effects on cell cycle regulators and gene expression underscore the mechanism of action.
- The specificity of the treatment for cancer cells highlights its potential therapeutic value.
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