The malignant phenotype of human papillomavirus (HPV)-positive cancer cells is maintained by the activity of the viral E6 and E7 genes. Here, we identified the polycomb group gene enhancer of zeste homologue 2 (EZH2) as a novel downstream target for the viral oncogenes in HPV-transformed cells. EZH2 expression was activated by HPV16 E7 at the transcriptional level via E7-mediated release of E2F from pocket proteins. RNA interference analyses showed that continuous EZH2 expression is required for the proliferation of HPV-positive tumor cells by stimulating cell cycle progression at the G 1 -S boundary. In addition to its growth-promoting activity, EZH2 also contributed to the apoptotic resistance of cervical cancer cells. Furthermore, we found that HPV-positive dysplastic and tumorigenic cervical lesions were characterized by high levels of EZH2 protein in vivo. We conclude that the E7 target gene EZH2 is a major determinant for the proliferation of HPVpositive cancer cells and contributes to their apoptotic resistance. Moreover, EZH2 may serve as a novel therapeutic target for the treatment of cervical cancer. [Cancer Res 2008;68(23):9964-72]

The enhancer of zeste homolog 2 (EZH2) gene has been recently linked to human malignancies where it may serve as a new target for cancer therapy. Here, we analyzed EZH2 expression in primary renal cell carcinoma (RCC) specimens and in nontumorous tissue samples from adult kidney. EZH2 transcripts were detectable in all RCC specimens examined. Expression levels were significantly higher in tumor tissue (p 0.0001) than in samples from normal adult kidney. Moreover, inhibition of endogenous EZH2 expression in RCC cell lines by RNA interference (RNAi) led to reduced proliferation and increased apoptosis in RCC cells. These data show that EZH2 is overexpressed in RCC. Furthermore, they indicate that the EZH2 gene plays a role for both the proliferation and the apoptosis resistance of RCC cells. Targeted inhibition of EZH2 could therefore represent a novel strategy to improve the therapeutic response of RCC. ' 2008 Wiley-Liss, Inc.Key words: renal cell carcinoma; enhancer of zeste homolog 2 (EZH2); RNA interference; tumor therapy Renal cell carcinoma (RCC) is estimated to account for more than 51,000 new cases and almost 13,000 cancer-related deaths in the United States in 2007, making it the second most lethal of the urological cancers. 1 RCCs typically are highly resistant toward chemotherapy with a concomitant poor prognosis in advanced stages. 2 Therefore, the identification of novel therapeutic targets and the development of new strategies for RCC treatment are urgently required.The enhancer of zeste homolog 2 (EZH2) gene encodes a polycomb group (PcG) protein, which acts as a histone methyltransferase 3-5 and also can directly control DNA methylation. 6 EZH2 is involved in several key regulatory mechanisms within eukaryotic cells, such as control of embryonal development or cell proliferation. 7,8 Moreover, there is accumulating evidence indicating that EZH2 may also play a pivotal role in the etiology of several tumor forms, which include prostate cancer 9,10 and breast cancer. 10,11 For both of these cancers, EZH2 expression is often observed in proliferative and more aggressive tumor subgroups and has diagnostic and/or prognostic value. [9][10][11] Notably, however, EZH2 appears to be not only a potential tumor marker but may itself contribute to the deregulation of cell growth as a bona fide oncogene. Overexpression of EZH2 conferred cellular growth advantage in vitro, 11-13 promoted invasion 11 and exhibited oncogenic properties in nude mice. 14 Vice versa, inhibition of EZH2 expression by antisense constructs or RNA interference (RNAi) did result in growth inhibition of some cancer cells. 9,15 Furthermore, RNAi-mediated inhibition of EZH2 expression induced anoikis in circulating prostate carcinoma precursor cells 16 and apoptotic cell death in breast cancer cells. 17 A possible role of EZH2 for RCC has not been studied so far. Here, we analyzed EZH2 expression in primary RCC specimens and in nontumorous tissue. In addition, we investigated the functional role of EZH2 for the proliferation control and apop...

The enhancer of zeste homolog 2 (EZH2) gene has been recently linked to human malignancies where it may serve as a new target for cancer therapy. Here, we analyzed EZH2 expression in primary renal cell carcinoma (RCC) specimens and in nontumorous tissue samples from adult kidney. EZH2 transcripts were detectable in all RCC specimens examined. Expression levels were significantly higher in tumor tissue (p ≤ 0.0001) than in samples from normal adult kidney. Moreover, inhibition of endogenous EZH2 expression in RCC cell lines by RNA interference (RNAi) led to reduced proliferation and increased apoptosis in RCC cells. These data show that EZH2 is overexpressed in RCC. Furthermore, they indicate that the EZH2 gene plays a role for both the proliferation and the apoptosis resistance of RCC cells. Targeted inhibition of EZH2 could therefore represent a novel strategy to improve the therapeutic response of RCC. © 2008 Wiley‐Liss, Inc.