CDK2-mediated site-specific phosphorylation of EZH2 drives and maintains triple-negative breast cancer

Lei Nie,Yi-Hsin Hsu,Dean N Pan,Yi Yang,Fei Zhang,Jung-Mao Hsu,Li-Chuan Chan,Weiya Xia,Wei‐Xia Lin ,Rong Deng,Gabriel N Hortobágyi ,How Wen Ko ,Yongtao Han ,Cihui Zhu,Jun Yao,Longfei Huo,Celina G Kleer,Yu Chu ,Baozhen Ke,Jun Tang,Yongkun Wei,Hirohito Yamaguchi,Xixi Zhao,J Hou ,Jennifer L Hsu,Nancy E Davidson,Mien‐Chie Hung

doi:10.1038/s41467-019-13105-5

Abstract

Triple-negative breast cancer (TNBC), which lacks estrogen receptor α (ERα), progesterone receptor, and human epidermal growth factor receptor 2 (HER2) expression, is closely related to basal-like breast cancer. Previously, we and others report that cyclin E/cyclin-dependent kinase 2 (CDK2) phosphorylates enhancer of zeste homolog 2 (EZH2) at T416 (pT416-EZH2). Here, we show that transgenic expression of phospho-mimicking EZH2 mutant EZH2T416D in mammary glands leads to tumors with TNBC phenotype. Coexpression of EZH2T416D in mammary epithelia of HER2/Neu transgenic mice reprograms HER2-driven luminal tumors into basal-like tumors. Pharmacological inhibition of CDK2 or EZH2 allows re-expression of ERα and converts TNBC to luminal ERα-positive, rendering TNBC cells targetable by tamoxifen. Furthermore, the combination of either CDK2 or EZH2 inhibitor with tamoxifen effectively suppresses tumor growth and markedly improves the survival of the mice bearing TNBC tumors, suggesting that the mechanism-based combination therapy may be an alternative approach to treat TNBC.

Highlights

(BLBC) subtype represents a majority of Triple-negative breast cancer (TNBC)
To examine whether expression of cyclin-dependent kinase 2 (CDK2)-activated enhancer of zeste homolog 2 (EZH2) in mammary glands contributes to basal-like mammary tumor development, we established a transgenic mouse model expressing phospho-mimicking EZH2T416D mutant (Tg-EZH2T416D) or wild-type EZH2 (Tg-EZH2WT) driven by the mouse mammary tumor virus (MMTV) promoter
Histology and whole-mount analyses on the mammary glands showed that nulliparous female transgenic mice at young age (

Summary

Introduction

(BLBC) subtype represents a majority of TNBC. Gene expression profiling indicates that 70–80% of TNBC fall under BLBC, a highly aggressive subtype that initially responds to chemotherapy but eventually develops resistance, metastasis, and post-surgical re-occurrence[2]. Targeted expression of wild-type EZH2 (EZH2WT) alone in mammary glands leads to hyperplasia without developing tumors in animal studies[12,13], whereas transgenic mice harboring mammary gland-specific expression of constitutively active CDK2 develop mammary tumors containing basal-like components[14]. These findings raise an interesting possibility that overexpression of EZH2 is not sufficient to drive mammary tumorigenesis and that persistent activation of EZH2 by cyclin E/CDK2-dependent phosphorylation may be a prerequisite for tumor development. GSK343 has high selectivity for EZH2 over other methyltransferases[17]

Methods

Results

Conclusion