Abstract
Increased levels of enhancer of zeste homolog 2 (EZH2), a critical regulator of cellular memory, are associated with negative estrogen receptor (ER) expression and disease progression in breast cancer. High levels of EZH2 signal the presence of metastasis and poor outcome in breast cancer patients. To test the hypothesis that deregulation of EZH2 contributes to ER-negative breast cancer progression, EZH2 expression was inhibited in ER-negative breast cancer cells MDA-MB-231 and CAL51 using a lentivirus system. EZH2 knockdown decreased proliferation and delayed the G2/M cell-cycle transition, although not affecting apoptosis. In vivo, EZH2 downregulation significantly decreased breast xenograft growth and improved survival. EZH2 knockdown upregulated BRCA1 protein. Of note, BRCA1 knockdown was sufficient to rescue the effects of EZH2 downregulation on proliferation, G2/M arrest, and on the levels of hyperphosphorylated mitotic Cdc25C and Cyclin B1 proteins, crucial for entry into mitosis. Invasive ER-negative breast carcinomas show significant overexpression of EZH2 and downregulation of BRCA1 proteins. Taken together, we show that EZH2 is important in ER-negative breast cancer growth in vivo and in vitro, and that BRCA1 is required for the proliferative effects of EZH2. Blockade of EZH2 may provide a prime target to prevent and/or halt ER-negative breast cancer progression.
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Acknowledgements
We thank Dr Arul Chinnaiyan for the EZH2 plasmid, and Tracey Filzen for technical support. We thank Robin Kunkel for assistance with artwork. We thank the University of Michigan Vector Core for virus generation. This work was supported by NIH grants CA090876 (CGK), CA107469 (CGK), CA77612 (SDM), a grant from the Avon Foundation (CGK), a grant from the Burroughs Wellcome Fund (SDM) and a grant from the Department of Defense Breast Cancer Research Program (ACV).
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Gonzalez, M., Li, X., Toy, K. et al. Downregulation of EZH2 decreases growth of estrogen receptor-negative invasive breast carcinoma and requires BRCA1. Oncogene 28, 843–853 (2009). https://doi.org/10.1038/onc.2008.433
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DOI: https://doi.org/10.1038/onc.2008.433
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