PolycombGroup Protein Enhancer of Zeste 2 Is an Oncogene That Promotes the Neoplastic Transformation of a Benign Prostatic Epithelial Cell Line

Polycomb group protein enhancer of zeste 2 (EZH2) is a master regulatory protein that plays a critical role in development as part of the polycomb repressive complex 2. Polycomb repressive complex 2 controls numerous cell cycle and regulatory genes through trimethylation of histone 3, which results in chromatin condensation and transcriptional silencing. EZH2 overexpression has been correlated with high incidence of more aggressive, metastatic prostate cancers. Although this correlation means EZH2 could prove valuable as a biomarker in clinical settings, the question remains whether EZH2 is actually responsible for the initiation of these more aggressive tumor types. In this study, EZH2-mediated neoplastic transformation of the normal prostate epithelial cell line benign prostate hyperplasia 1 (BPH1) was confirmed by in vivo tumor growth and in vitro colony formation. Furthermore, EZH2 transformation resulted in increased invasive behavior of BPH1 cells, indicating that EZH2 may be responsible for aggressive behavior in prostate cancers. BPH1 was also transformed with the classic oncogenes myristoylated Akt and activated Ras(V12) to allow phenotype comparisons with the EZH2-transformed cells. This study marks the first demonstration of neoplastic transformation in prostate cells mediated by EZH2 and establishes that EZH2 possesses stronger transforming activity than Akt but weaker activity than activated Ras. (Mol Cancer Res 2009;7(9):1456–65) Introduction Polycomb group (PcG) protein enhancer of zeste 2 (EZH2) was first identified for its master regulatory role over the homeobox genes during development. By controlling spatial and temporal expression of various developmental genes, EZH2 and its family members determine body patterning and cell fate (1, 2). Within the polycomb group family exist two complexes: polycomb repressive complex 1 (PRC1) and polycomb repressive complex 2 (PRC2), the latter of which is composed of EZH2 and its binding partners EED and Su(z)12 (3, 4). PRC2 is expressed by proliferating cells and is responsible for silencing target genes through trimethylation of lysine 27 on histone 3 (5-9). EZH2 is the member of PRC2 responsible for the methyltransferase activity via the COOH-terminal SET domain (10). EZH2 was implicated in cancer aggression when it was found to be expressed at very high levels in proliferating mantle cell lymphoma samples (11). Soon thereafter, a gene array comparing benign and metastatic prostate cancer samples found that EZH2 was consistently overexpressed in metastatic cancer (12). Furthermore, EZH2 expression levels were found to be predictive of metastatic behavior in early-stage, organconfined prostate cancers. Subsequently, EZH2 was found to be overexpressed in the more aggressive forms of breast (13, 14), endometrium (15), melanoma (16), myeloma (17), and gastric (18) cancers, to name a few (19). Additional evidence regarding EZH2 and its relationship to prostate cancer aggression continued to inundate the field. In situ hybridization experiments on advanced-stage prostate cancer samples found that, in many cases, EZH2 overexpression was possibly due to gene amplification (20) or a loss of microRNA-mediated inhibition (21). EZH2 was also validated as a biomarker that could be used to determine risk of prostate cancer recurrence in patients (22-24). Furthermore, it was confirmed that EZH2 was involved in maintaining proliferation and invasive behavior of some prostate cancer cell lines (25). Despite this abundance of data on prostate cancer and prostate cancer cell lines, little work has been done to examine the role of EZH2 in cancer initiation. One study showed that EZH2 promoted transformation of breast epithelial cells (26), but a parallel work in prostate epithelial cells has not been done. However, tissue-specific differences between breast and prostate cells indicate that a transformation study in prostate cells is warranted. For instance, androgen receptor, which is critical Received 3/20/09; revised 6/18/09; accepted 7/6/09; published OnlineFirst 9/1/09. Grant support: University of California at Los Angeles Specialized Program of Research Excellence in Prostate Cancer Career Development Award (B.D.W. Karanikolas). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: Supplementary data for this article are available at Molecular Cancer Research Online (http://mcr.aacrjournals.org/). Requests for reprints: Lily Wu, Departments of Molecular and Medical Pharmacology and Urology, University of California at Los Angeles, CHS 33118, Box 951735, Los Angeles, California 90095-1738. Phone: 310-825-8511; Fax: 310-206-5343. E-mail: LWu@mednet.ucla. edu Copyright © 2009 American Association for Cancer Research. doi:10.1158/1541-7786.MCR-09-0121 Mol Cancer Res 2009;7(9). September 2009 1456 on August 4, 2017. © 2009 American Association for Cancer Research. mcr.aacrjournals. org Downloaded from Published OnlineFirst September 1, 2009; DOI: 10.1158/1541-7786.MCR-09-0121