First Department of Medicine, Hokkaido University School of Medicine, Sapporo, Japan.
Lung Cancer. 2012 Nov;78(2):138-43. doi: 10.1016/j.lungcan.2012.08.003. Epub 2012 Aug 25.
EZH2 (enhancer of zeste homolog 2) is the catalytic subunit of PRC2 (polycomb repressive complex 2), which mediates histone methyltransferase activity and functions as transcriptional repressor involved in gene silencing. EZH2 is involved in malignant transformation and biological aggressiveness of several human malignancies. We previously demonstrated that non-small cell lung cancers (NSCLCs) also overexpress EZH2 and that high expression of EZH2 correlates with poor prognosis. Growing evidence indicates that EZH2 may be an appropriate therapeutic target in malignancies, including NSCLCs. Recently, an S-adenosyl-l-homocysteine hydrolase inhibitor, 3-Deazaneplanocin A (DZNep), has been shown to deplete and inhibit EZH2. The aim of this study was to determine the effect of DZNep in NSCLC cells. Knockdown of EZH2 by small-interfering RNA (siRNA) resulted in decreased growth of four NSCLC cell lines. MTT assays demonstrated that DZNep treatment resulted in dose-dependent inhibition of proliferation in the NSCLC cell lines with a half maximal inhibitory concentration (IC50) ranging from 0.08 to 0.24 μM. Immortalized but non-cancerous bronchial epithelial and fibroblast cell lines were less sensitive to DZNep than the NSCLC cell lines. Soft agarose assays demonstrated that anchorage-independent growth was also reduced in all three NSCLC cell lines that were evaluated using this assay. Flow cytometry analysis demonstrated that DZNep induced apoptosis and G1 cell cycle arrest in NSCLC cells, which was partially associated with cyclin A decrease and p27(Kip1) accumulation. DZNep depleted cellular levels of EZH2 and inhibited the associated histone H3 lysine 27 trimethylation. These results indicated that an epigenetic therapy that pharmacologically targets EZH2 via DZNep may constitute a novel approach to treatment of NSCLCs.
EZH2（增强子的锌指蛋白 2）是 PRC2（多梳抑制复合物 2）的催化亚基，它介导组蛋白甲基转移酶活性，并作为参与基因沉默的转录抑制因子发挥作用。EZH2 参与几种人类恶性肿瘤的恶性转化和生物学侵袭性。我们之前证明非小细胞肺癌（NSCLC）也过表达 EZH2，并且 EZH2 的高表达与预后不良相关。越来越多的证据表明，EZH2 可能是包括 NSCLC 在内的恶性肿瘤的合适治疗靶点。最近，一种 S-腺苷-L-同型半胱氨酸水解酶抑制剂 3-去氮杂胞苷 A（DZNep）已被证明可以耗尽并抑制 EZH2。本研究旨在确定 DZNep 在 NSCLC 细胞中的作用。通过小干扰 RNA（siRNA）敲低 EZH2 导致四种 NSCLC 细胞系的生长减少。MTT 测定表明，DZNep 处理导致 NSCLC 细胞系的增殖呈剂量依赖性抑制，半数最大抑制浓度（IC50）范围为 0.08 至 0.24 μM。与 NSCLC 细胞系相比，永生化但非癌性支气管上皮和成纤维细胞系对 DZNep 的敏感性较低。软琼脂糖测定表明，在使用该测定法评估的所有三种 NSCLC 细胞系中，锚定非依赖性生长也减少。流式细胞术分析表明，DZNep 诱导 NSCLC 细胞凋亡和 G1 细胞周期停滞，这部分与细胞周期蛋白 A 减少和 p27（Kip1）积累有关。DZNep 耗尽细胞内 EZH2 水平并抑制相关的组蛋白 H3 赖氨酸 27 三甲基化。这些结果表明，通过 DZNep 药理学靶向 EZH2 的表观遗传治疗可能构成 NSCLC 治疗的新方法。
