Abstract 2895: Phosphorylation of EZH2 at T416 by CDK2 promotes development of mammary tumors with basal-like phenotype

Abstract

Abstract Basal-like breast cancer, also referred to as triple negative breast cancer (TNBC) due to the lack of expression of ErbB2, PR, and ER alpha receptors, is considered to be one of the most aggressive breast cancers, which display high rates of tumor cell proliferation, metastasis, and post-surgical re-occurrence. This subtype of breast cancer presents a major challenge for breast cancer oncologists as currently there is no effective therapy available. Here, we show that Cyclin E and EZH2, the methyltransferase component of the polycomb repressive complex 2 (PRC2) are exclusively co-expressed in TNBC tumor tissues. We further show that CDK2, the only known enzymatic partner of Cyclin E, can phosphorylate EZH2 at T416 in vivo. CDK2-mediated modification of EZH2 at T416 leads to gain-of-function, enhancing its ability to promote breast cancer cell migration/invasion, expansion and self-renewal of tumor sphere in vitro, and tumor growth in vivo. In addition, our immunohistochemistry-staining of 247 primary breast tumor tissues validates that high EZH2/T416 phosphorylation correlates with poor survival in TNBC but not in non-TNBC patients. To further attest the oncogenic role of EZH2/T416 phosphorylation by CDK2 in vivo, we generated transgenic mice expressing EZH2T416D mutant, a mimicking phosphorylated form of EZH2, in mammary glands. In contrast to previously reported EZH2WT transgenic mice, which did not develop mammary tumors, our EZH2T416D-expressing mice developed malignant mammary tumor with basal-like and highly metastatic potential phenotypes. These genetic evidence revealed that CDK2/Cyclin E mediated site-specific phosphorylation of EZH2 is capable of inducing the basal-like/TNBC phenotype and maintaining cancer stem cell population of breast cancers so that the T416 phosphorylation of EZH2 might serve as a biomarker for TNBC prognosis and effective therapy. Citation Format: Lei Nie, Yongkun Wei, Adam LaBaff, Cheng-Chieh Yang, Weiya Xia, Longfei Huo, Dongping Liu, Yi-Hsin Hsu, Gabriel N. Hortobagyi, Jun Yao, Celina G. Kleer, Mien-Chie Hung. Phosphorylation of EZH2 at T416 by CDK2 promotes development of mammary tumors with basal-like phenotype. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2895. doi:10.1158/1538-7445.AM2015-2895