• Jie Niu, Xiao Wang, Chao Liang, Yi-Dan Zhang, Fan-Ye Liu, Hai-Ying Li, Song-Qiang Xie, Hua Sun, and Dong Fang.
• School of Pharmacy, Institute for Innovative Drug Design and Evaluation, Henan University, N. Jinming Ave, 475004 Kaifeng, China.
• Cell Biol. Int. 2019 Aug 1; 43 (8): 931-939.

AbstractPhosphoinositide 3-kinase (PI3K) signaling is frequently deregulated in breast cancer and plays a critical role in tumor progression. However, resistance to PI3K inhibitors in breast cancer has emerged, which is due to the enhanced β-catenin nuclear accumulation. Until now, the mechanisms underlying PI3K inhibition-induced β-catenin nuclear accumulation remains largely unknown. In the present study, we found inhibition of PI3K with LY294002 promoted β-catenin nuclear accumulation in MCF-7 and MDA-MB-231 breast cancer cells. Combining PI3K inhibitor LY294002 with XAV-939, an inhibitor against β-catenin nuclear accumulation, produced an additive anti-proliferation effect against breast cancer cells. Subsequent experiments suggested β-catenin nuclear accumulation induced by PI3K inhibition depended on the feedback activation of epidermal growth factor receptor (EGFR) signaling pathway in breast cancer cells. Inhibition of EGFR phosphorylation with Gefitinib enhanced anti-proliferation effect of PI3K inhibitor LY294002 in MCF-7 and MDA-MB-231 cells. Taken together, our findings may elucidate a possible mechanism explaining the poor outcome of PI3K inhibitors in breast cancer treatment.© 2019 International Federation for Cell Biology.

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