Abstract 3333: Overexpression of EZH2 accelerates ERB2 driven tumorigenesis in the mammary gland
Authors: Li Xin , DuPrie Matthew , Krueger Heather , Kleer Celina G. 
Published: June 2012

BACKGROUND: EZH2 protein is overexpressed mainly in ER- tumors with concomitant HER-2/neu overexpression and/or p53 mutations and is an independent predictor of metastasis and death. A role for EZH2 in stem cell maintenance was recently reported. We previously demonstrated that mammary specific EZH2 overexpression causes ductal hyperbranching and intraductal hyperplasia but is not sufficient in isolation to induce carcinomas. To address the biological impact of EZH2 overexpression in mammary tumorigenesis, we generated a novel transgenic mouse model by crossing transgenic mice carrying mouse mammary tumor virus/EZH2 (MMTV-EZH2) and MMTV-inactivated neu (MMTV-neu) to derive progeny that coexpress the transgenes in the mammary epithelium (EZH2+ neu).

METHODS: MMTV-neu mice were purchased from Jackson laboratories (FVB/N-TgN (MMTVneu)202 Mul/J, or MMTV neu, stock number 002376). They are homozygous for the MMTV neu (rat) transgene, and overexpress the neu proto-oncogene under the control of the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). We used synchronized breeding methods with male EZH2 heterozygous transgenic mice and female MMTV-neu transgenic mice to obtain EZH2+; neu and EZH2 wt; neu mice. Mouse handling and experimental procedures were conducted in accordance with the NIH Guide for the Care and Use of Laboratory Animals and were approved by the IACUC of the UM. Tumors were measured with a caliper. Statistical analyses of tumor initiation time were performed. Flow cytometry and western blot were performed in mouse mammary glands and MCF10A cells.

RESULTS: EZH2 overexpression accelerates the process of ErbB-2-mediated mammary tumorigenesis. EZH2+ neu mice (n=30) showed accelerated tumor initiation (median time to tumor initiation=234 days) than EZH2 wt neu control group (n=25) (median time to tumor initiation=295 days) (Log-rank p-value &lt; 0.0001). Despite no differences in the size of the tumors or tumor histology, flow cytometry analysis revealed that EZH2+; neu bitransgenic mice had an expansion of the luminal progenitor cell population (CD24+CD29loCD61+) in the mammary glands at 8 weeks of age, preceding tumor development. This was associated with upregulation of the luminal progenitor regulator STAT5 mRNA, protein, and signaling pathway. Consistently, conditional EZH2 overepresssion in MCF10A cells showed expansion of the luminal progenitor population (CD49f+EpCAM+).

CONCLUSION: Our experiments demonstrate that overexpression of EZH2 accelerates the initiation of ErbB2-induced mammary tumors and lead to the novel hypothesis that EZH2 overexpression activates STAT5 signaling pathway to expand mammary luminal progenitor cells, which is under investigation in our lab.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3333. doi:10.1158/1538-7445.AM2011-3333