新兴抗肿瘤靶点EZH2作用机制及研究进展

zeste基因同源蛋白2(enhancer of zeste homolog 2,EZH2)是由EZH2基因编码的一种赖氨酸特异性组蛋白甲基转移酶（histone-lysine N-methyltransferase,HRX),是多梳家族蛋白(polycomb-group proteins,PcGs)家族的重要组分。该基因正常状态下参与胚胎干细胞发育,维持正常细胞分化,在两性发育中驱动女性一个X染色体的沉默,在造血过程中维持B淋巴细胞和T淋巴细胞的未分化状态。病理状态下,EZH2成为一种基因抑制因子,当它过度表达时,组蛋白的三甲基化导致许多正常开启的肿瘤抑制因子被关闭。在多种肿瘤组织中EZH2含量明显高于癌旁组织,预后差的肿瘤中EZH2表达含量明显高于预后良好的肿瘤。因此,抑制EZH2的表达很可能是未来癌症治疗的一个有希望的策略。本文就目前研究状况做一简要综述。     

EZH2在乳腺癌中的差异表达及临床意义

目的:利用整合生物信息学手段分析EZH2（enhancer of zeste 2 polycomb repressive complex 2 subunit）基因在乳腺癌中的表达及其临床意义。方法:在肿瘤基因组计划数据库（The Cancer Genome Atlas,TCGA）中下载乳腺癌与正常乳腺组织的基因表达谱数据,进一步利用Ualcan数据库和人类蛋白质图谱（The Human Protein Atlas）数据库数据分析EZH2基因在乳腺癌中的mRNA及蛋白表达水平。利用Ualcan数据库分析EZH2基因的甲基化水平并筛选其共表达基因;对EZH2及其共表达基因进行GO（Gene Ontology）富集分析和KEGG通路分析以明确EZH2的共表达基因参与的生物学过程和相关通路;使用Kaplan-Meier生存分析法分析乳腺癌患者的总生存期、无病生存期、无远处转移生存期及后进展生存期与EZH2基因表达水平的关系并绘制生存曲线。结果:与正常乳腺组织相比,EZH2在乳腺癌组织中的mRNA及蛋白表达量明显升高。而EZH2的甲基化程度在乳腺癌组织与正常乳腺组织中则差异不明显。同时,EZH2的表达水平与年龄、乳腺癌分期及乳腺癌分子分型等因素密切相关。EZH2及其共表达基因主要参与了核碱基的调节、细胞周期调控、染色体分离、DNA复制、DNA修复等生物学过程,并参与了细胞周期、DNA 复制、M/G1期转化、M期、有丝分裂前中期、ATM通路等生物学通路。此外,EZH2基因表达水平高的乳腺癌患者的总生存期、无病生存期、无远处转移生存期及后进展生存期均明显低于EZH2基因低表达的患者。结论:EZH2在乳腺癌组织中高表达并且与患者不良预后密切相关。同时,EZH2的表达水平与乳腺癌的发生、发展密切相关。EZH2在乳腺癌诊断、靶向治疗及预后分析中具有重要的临床意义。     

siRNA转染复合物对卵巢癌细胞SKOV3裸鼠模型EZH2的影响

目的：利用siRNA载体介导的RNA干扰技术靶向沉默EZH2基因,从而观察对卵巢癌裸鼠模型中肿瘤组织EZH2 mRNA的表达水平,探讨siRNA转染之后,EZH2对肿瘤组织黏附、侵袭和转移的作用。方法：采用原位造模方式,即人卵巢癌细胞SKOV3移植方法构建卵巢癌裸鼠模型。将30只卵巢癌裸鼠随机分为3组（n=10）：siRNA干扰（EZH2-siRNA组）组、阴性对照组（NC-siRNA组）和空白对照组（Con组）,前两组每日分别腹腔注射100μl siRNA转染复合物和阴性对照转染复合物（1次,共注射5次。末次腹腔注射后48h断颈处死裸鼠,观察腹腔肿瘤组织病灶形成情况,取肿瘤病灶标本。RT-PCR和Western blotting检测肿瘤组织EZH2 mRNA与蛋白表达水平。结果：实验裸鼠共35只,30只造模成功。RT-PCR检测结果显示,与NC-siRNA组和Con组相比,EZH2-siRNA组EZH2 mRNA表达水平明显下降（P〈0.05）,而后两者之间差异无统计学意义（P〉0.05）。Western blotting结果显示,EZH2-siRNA组EZH2蛋白表达明显减弱（P〈0.05）,而后两者之间差异无统计学意义（P〉0.05）。结论：EZH2基因siRNA转染之后的肿瘤组织中EZH2 mRNA与蛋白表达明显减弱siRNA转染之后的肿瘤组织的侵袭、转移能力明显下降,EZH2基因表达减弱可以作为基因治疗的新手段。     

EZH2基因在消化系统肿瘤中的研究进展

多梳抑制复合物2(PRC2)是一种作用于组蛋白H3赖氨酸位点K27的高度保守的组蛋白甲基转移酶,是PcG蛋白家族的一员.而PRC2的催化亚基是果蝇Zeste基因增强子同源物2(EZH2).大量研究证明,EZH2在多种肿瘤组织中高表达,例如乳腺癌、非小细胞肺癌、胃癌等.本文总结了EZH2基因的起源、结构、生物学功能及其在消化系统肿瘤中的研究进展,并对EZH2的靶向治疗进行展望.     

EZH2与肿瘤的关系

 EZH2是PRC2的一个亚基,通过催化组蛋白H3第27位赖氨酸三甲基化抑制基因表达。在前列腺癌、乳腺癌、膀胱癌及胃癌等多种肿瘤中都有高表达,与肿瘤的恶性进程、侵袭性、转移能力关系密切。随着对其在肿瘤中分子功能、上下游调控机制、临床病理特点的深入了解,EZH2有望做为靶点,为肿瘤治疗提供新的途径。     

zeste基因增强子同源物2在乳腺癌中的研究现状

zeste基因增强子同源物2(EZH2)是果蝇zeste基因增强子[E(z)]的人类同源物组蛋白甲基化的重要工具酶,也是多梳基因家族PcG(polycomb group)的核心成员。EZH2参与多梳蛋白复合体2的形成,促使相应组蛋白甲基化,从表观遗传学的角度介导相应靶基因沉默,在肿瘤的发生、发展过程中发挥着重要作用。其高表达与多种恶性肿瘤的发生、发展和极差的预后密切相关。近年来,越来越多的学者对EZH2的致癌机制进行了深入研究,为乳腺癌转移的检测、预后评估及治疗提供了全新的思路。笔者就EZH2表达情况及其与乳腺癌发生、发展、转移及预后之间的关系作一综述,以便临床医师更好地认识这一新的肿瘤标志物。     

EZH2 和PTEN在膀胱癌的表达及预后分析

目的:研究膀胱癌组织EZH2 和PTEN基因的表达,探讨其与膀胱癌临床病理特征及无瘤生存的关系。方法:制作80例膀胱移行细胞癌和10例正常膀胱黏膜（对照组）组织芯片,应用免疫组织化学方法检测EZH 2 和PTEN蛋白的表达,采用Kaplan-Meier 单因素和Cox 比例风险模型多因素分析其与膀胱癌无瘤生存的关系。结果:膀胱癌组织中EZH 2 和PTEN阳性表达率分别为80.0% 和45.0% 。EZH 2 和PTEN的阳性表达率在膀胱癌不同临床分期及病理分级组间存在显著性差异（P<0.05）,且两者的表达呈负相关（P=0.033）。 全组膀胱癌患者术后平均无瘤生存期为39.4 个月,1、3、5 年无瘤生存率分别为70.0% 、55.2% 、41.4% 。单因素分析表明:病理分级、肿瘤数目和EZH 2 表达为影响膀胱癌预后的相关因素;多因素分析表明:病理分级、肿瘤数目和EZH 2 表达是膀胱癌复发的独立危险因素。结论:EZH 2 和PTEN异常表达与膀胱癌的发生、发展关系密切。病理分级、肿瘤数目和EZH 2 是膀胱癌预后的独立危险因素。      

zeste基因增强子同源物2在血液系统肿瘤中的研究进展

zeste基因增强子同源物2(EZH2)是一种组蛋白甲基转移酶, 在组蛋白甲基化修饰中研究较为广泛, 其可促进基因的表观遗传学基因沉默, 并通过多种调控机制介导肿瘤的发生。EZH2的功能获得和丧失突变在许多癌症中已被证实。目前, 随着EZH2在表观遗传机制中的调控作用得到广泛重视, EZH2失调影响血液系统恶性肿瘤发病机制的确切方式仍有待阐明。文章对EZH2在血液系统肿瘤中的致病作用进行综述, 以期为血液系统肿瘤的防治寻找新的靶点。     

下调EZH2基因对胃癌细胞株SGC7901增殖作用的影响

目的 探讨下调EZH2基因对胃癌细胞株SGC7901的增殖作用,研究EZH2基因在胃癌发生发展中的作用.方法 针对EZH2基因序列设计合成小干扰RNA片段(siRNA)及无效序列片段,将EZH2 siRNA转染至胃癌细胞株SGC7901中作为干扰组,以转染无效序列片段作为阴性对照组,以未作任何处理组作为空白对照组,采用荧光定量PCR(qRT-PCR)检测EZH2基因下调后EZH2 mRNA的表达,采用Western blot法检测EZH2蛋白表达量,采用CCK-8法检测细胞增殖的活性.结果 成功转染EZH2 siRNA至胃癌SGC7901细胞,干扰组的EZH2 mRNA和蛋白相对表达量较阴性对照组及空白对照组下降,且干扰组细胞增殖受到抑制.结论 下调EZH2基因的表达,使胃癌细胞增殖受到抑制,说明EZH2基因在胃癌细胞的增殖发展进程中有很重要的意义,为深入研究胃癌基因治疗提供一定的理论依据.     

沉默EZH2对胃癌MKN-28细胞增殖和侵袭的影响

目的:探讨EZH2对胃癌MKN-28细胞生物学的影响.方法:siRNA干扰EZH2;MTT法检测沉默EZH2后细胞的增殖情况;Transwell小室观察细胞的侵袭情况;Realtime-PCR检测细胞中相关基因的表达情况.结果:siRNA有效干扰了EZH2的表达;沉默EZH2细胞组的细胞增殖明显受到抑制(P<0.05);细胞的侵袭情况,沉默EZH2明显抑制了细胞的侵袭,与其他两组比较差异显著(P<0.05);siEZH2细胞组E-cadherin mRNA、β-catenin mRNA的表达水平高于其他两组,Bcl-2 mRNA的表达水平低于其他两组(P<0.05).结论:沉默EZH2抑制了胃癌MKN-28细胞的增殖,抑制了细胞的侵袭和抗凋亡基因的表达,可能是通过调控E-cadherin的表达水平和Wnt信号途径实现的,为寻找有效的靶点和肿瘤的靶向治疗提供一定的理论依据.     

Validation of the histone methyltransferase EZH2 as a therapeutic target for various types of human cancer and as a prognostic marker

The emphasis in anticancer drug discovery has always been on finding a drug with great antitumor potential but few side-effects. This can be achieved if the drug is specific for a molecular site found only in tumor cells. Here, we find the enhancer of zeste homolog 2 (EZH2) to be highly overexpressed in lung and other cancers, and show that EZH2 is integral to proliferation in cancer cells. Quantitative real-time PCR analysis revealed higher expression of EZH2 in clinical bladder cancer tissues than in corresponding non-neoplastic tissues (P < 0.0001), and we confirmed that a wide range of cancers also overexpress EZH2, using cDNA microarray analysis. Immunohistochemical analysis showed positive staining for EZH2 in 14 of 29 cases of bladder cancer, 135 of 292 cases of non-small-cell lung cancer (NSCLC), and 214 of 245 cases of colorectal cancer, whereas no significant staining was observed in various normal tissues. We found elevated expression of EZH2 to be associated with poor prognosis for patients with NSCLC (P = 0.0239). In lung and bladder cancer cells overexpressing EZH2, suppression of EZH2 using specific siRNAs inhibited incorporation of BrdU and resulted in significant suppression of cell growth, even though no significant effect was observed in the normal cell strain CCD-18Co, which has undetectable EZH2. Because EZH2 expression was scarcely detectable in all normal tissues we examined, EZH2 shows promise as a tumor-specific therapeutic target. Furthermore, as elevated levels of EZH2 are associated with poor prognosis of patients with NSCLC, its overexpression in resected specimens could prove a useful molecular marker, indicating the necessity for a more extensive follow-up in some lung cancer patients after surgical treatment.     

The tumor suppressor gene rap1GAP is silenced by miR-101-mediated EZH2 overexpression in invasive squamous cell carcinoma

Rap1GAP is a critical tumor suppressor gene that is downregulated in multiple aggressive cancers, such as head and neck squamous cell carcinoma, melanoma and pancreatic cancer. However, the mechanistic basis of rap1GAP downregulation in cancers is poorly understood. By employing an integrative approach, we demonstrate polycomb-mediated repression of rap1GAP that involves Enhancer of Zeste Homolog 2 (EZH2), a histone methyltransferase in head and neck cancers. We further demonstrate that the loss of miR-101 expression correlates with EZH2 upregulation, and the concomitant downregulation of rap1GAP in head and neck cancers. EZH2 represses rap1GAP by facilitating the trimethylation of histone 3 at lysine 27, a mark of gene repression, and also hypermethylation of rap1GAP promoter. These results provide a conceptual framework involving a microRNA-oncogene-tumor suppressor axis to understand head and neck cancer progression.     

Curcumin analogue CDF inhibits pancreatic tumor growth by switching on suppressor microRNAs and attenuating EZH2 expression

The histone methyltransferase EZH2 is a central epigenetic regulator of cell survival, proliferation, and cancer stem cell (CSC) function. EZH2 expression is increased in various human cancers, including highly aggressive pancreatic cancers, but the mechanisms underlying for its biologic effects are not yet well understood. In this study, we probed EZH2 function in pancreatic cancer using diflourinated-curcumin (CDF), a novel analogue of the turmeric spice component curcumin that has antioxidant properties. CDF decreased pancreatic cancer cell survival, clonogenicity, formation of pancreatospheres, invasive cell migration, and CSC function in human pancreatic cancer cells. These effects were associated with decreased expression of EZH2 and increased expression of a panel of tumor-suppressive microRNAs (miRNA), including let-7a, b, c, d, miR-26a, miR-101, miR-146a, andmiR-200b, c that are typically lost in pancreatic cancer. Mechanistic investigations revealed that reexpression of miR-101 was sufficient to limit the expression of EZH2 and the proinvasive cell surface adhesion molecule EpCAM. In an orthotopic xenograft model of human pancreatic cancer, administration of CDF inhibited tumor growth in a manner associated with reduced expression of EZH2, Notch-1, CD44, EpCAM, and Nanog and increased expression of let-7, miR-26a, and miR-101. Taken together, our results indicated that CDF inhibited pancreatic cancer tumor growth and aggressiveness by targeting an EZH2-miRNA regulatory circuit for epigenetically controlled gene expression.     

Expression changes in EZH2, but not in BMI-1, SIRT1, DNMT1 or DNMT3B are associated with DNA methylation changes in prostate cancer

The polycomb proteins BMI-1, EZH2, and SIRT1 are characteristic components of the PRC1, PRC2, and PRC4 repressor complexes, respectively, that modify chromatin. Moreover, EZH2 may influence DNA methylation by direct interaction with DNA methyltransferases. EZH2 expression increases during prostate cancer progression, whereas BMI-1 and SIRT1 are not well investigated. Like EZH2 expression, DNA methylation alterations escalate in higher stage prostate cancers, raising the question whether these epigenetic changes are related. Expression of EZH2, BMI-1, SIRT1, and the DNA methyltransferases DNMT1 and DNMT3B measured by qRT-PCR in 47 primary prostate cancers was compared to APC, ASC, GSTP1, RARB2, and RASSF1A hypermethylation and LINE-1 hypomethylation. SIRT1 and DNMT3B were overexpressed in cancerous over benign tissues, whereas BMI-1 was rather downregulated and DNMT1 significantly diminished. Nevertheless, cancers with higher DNMT1 and BMI-1 expression had worse clinical characteristics, as did those with elevated EZH2. In particular, above median DNMT1 expression predicted a worse prognosis. EZH2 and SIRT1 overexpression were well correlated with increased MKI67. Immunohistochemistry confirmed limited EZH2 and heterogeneous DNMT3B overexpression and explained the decrease in BMI-1 by pronounced heterogeneity among tumor cells. EZH2 overexpression, specifically among all factors investigated, was associated with more frequent hypermethylation, in particular of GSTP1 and RARB2, and also with LINE-1 hypomethylation. Our data reveal complex changes in the composition of polycomb repressor complexes in prostate cancer. Heterogeneously expressed BMI-1 and slightly increased EZH2 may characterize less malignant cancers, whereas more aggressive cases express both at higher levels. SIRT1 appears to be generally increased in prostate cancers. Intriguingly, our data suggest a direct influence of increased EZH2 on altered DNA methylation patterns in prostate cancer.     

Collaboration of Kras and Androgen Receptor Signaling Stimulates EZH2 Expression and Tumor-Propagating Cells in Prostate Cancer

Elevation of the chromatin repression factor enhancer of zeste homolog (EZH2) is associated with progression and poor prognosis in several human cancers including prostate cancer. However, the mechanisms driving EZH2 expression are not fully understood. In this study, we investigated the functional synergy in prostate cancers in mice resulting from activation of the androgen receptor, Kras, and Akt, which drives three of the most frequently activated oncogenic signaling pathways in prostate cancer. Although, any two of these three events were sufficient to promote the formation and progression of prostate cancer, only the synergy of androgen receptor and Kras signaling could elevate EZH2 expression and expand prostate cancer progenitor cells in vivo. Our findings have revealed a genetic mechanism resulting in enhanced EZH2 expression during the progression of aggressive prostate cancer, with important implications for understanding how to target advanced disease where cancer progenitor cells may be critical. Cancer Res; 72(18); 4672-81. ?2012 AACR.