吉林大学学报(医学版)  2019, Vol. 45 Issue (05): 1036-1040     DOI: 10.13481/j.1671-587x.20190511

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赵丽艳, 宋扬, 陈勇, 贾茗博, 李蕴潜
ZHAO Liyan, SONG Yang, CHEN Yong, JIA Mingbo, LI Yunqian
沉默ZEB1基因对胶质瘤U87细胞上皮-间质转化的影响
Effect of silencing ZEB1 gene on epithelial to mesenchymal transition in glioma U87 cells
吉林大学学报(医学版), 2019, 45(05): 1036-1040
Journal of Jilin University (Medicine Edition), 2019, 45(05): 1036-1040
10.13481/j.1671-587x.20190511

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收稿日期: 2019-01-18
沉默ZEB1基因对胶质瘤U87细胞上皮-间质转化的影响
赵丽艳1 , 宋扬2 , 陈勇2 , 贾茗博1 , 李蕴潜2     
1. 吉林大学第二医院检验科, 吉林 长春 130041;
2. 吉林大学第一医院神经外科, 吉林 长春 130021
[摘要]: 目的: 探讨沉默锌指E盒结合同源框1(ZEB1)基因对胶质瘤U87细胞间质标志物表达和细胞迁移的作用,阐明ZEB1对胶质瘤细胞上皮-间质转化(EMT)的影响。方法: 将构建的ZEB1短发夹RNA(shRNA)干扰质粒(shZEB1#1和shZEB1#2)和对照质粒(shCtrl)转染至胶质瘤U87细胞,Western blotting法检测干扰效果。将胶质瘤U87细胞分为对照组(转染shCtrl的胶质瘤U87细胞)、EMT组[转染shCtrl的胶质瘤U87细胞用转化生长因子β1(TGF-β1)诱导EMT]和ZEB1基因沉默组(转染shZEB1的胶质瘤U87细胞用TGF-β1诱导EMT)。Western blotting法检测各组细胞中间质标志物(N-钙黏蛋白和波形蛋白)及基质金属蛋白酶9(MMP-9)的蛋白表达水平,划痕愈合实验检测各组细胞的迁移率。结果: Western blotting法检测,转染shZEB1#1和shZEB1#2的胶质瘤U87细胞中ZEB1蛋白表达水平较转染shCtrl的细胞明显降低(P < 0.05或P < 0.01),shZEB1#2对ZEB1表达的抑制效果更明显,表明ZEB1已稳定转染到U87细胞。与对照组比较,EMT组胶质瘤U87细胞中N-钙黏蛋白、波形蛋白和MMP-9蛋白表达水平均明显升高(P < 0.05或P < 0.01);与EMT组比较,ZEB1基因沉默组N-钙黏蛋白、波形蛋白和MMP-9蛋白表达水平明显降低(P < 0.05或P < 0.01)。EMT组细胞迁移率明显高于对照组(P < 0.01),而ZEB1基因沉默组细胞迁移率明显低于EMT组(P < 0.01)。结论: 沉默ZEB1基因表达可抑制胶质瘤U87细胞EMT,并降低细胞迁移能力,提示ZEB1可作为侵袭性胶质瘤治疗的重要靶标。
关键词: 锌指E盒结合同源框    基因沉默    胶质瘤U87细胞    上皮-间质转化    细胞迁移    
Effect of silencing ZEB1 gene on epithelial to mesenchymal transition in glioma U87 cells
ZHAO Liyan1 , SONG Yang2 , CHEN Yong2 , JIA Mingbo1 , LI Yunqian2     
1. Department of Medical Laboratory, Second Hospital, Jilin University, Changchun 130041, China;
2. Department of Neurosurgery, First Hospital, Jilin University, Changchun 130021, China
[ABSTRACT]: Objective: To investigate the effects of silencing zinc finger E-box binding homeobox1(ZEB1) gene on the expressions of mesenchymal markers and cell migration in the glioma U87 cells, and to clarify the effect of ZEB1 on the epithelial to mesenchymal transition (EMT) in the glioma cells. Methods: The constructed ZEB1 shRNA interfering plasmid and control plasmid (shCtrl) were transfected into the glioma U87 cells and the interfering effects were detected by Western blotting method. The glioma U87 cells were divided into control group (the glioma U87 cells were transfected with shCtrl), EMT group (EMT was induced by TGF-β1 in the glioma U87 cells transfected with shCtrl) and ZEB1 silence group (EMT was induced by TGF-β1 in the glioma U87 cells transfected with ZEB1 shRNAs plasmid). The protein expression levels of mesenchymal markers (N-cadherin, Vimentin), and matrix metalloproteinase-9 (MMP-9) in the glioma U87 cells were measured by Western blotting method. The scratch-healing assay was performed to examine the migration ability of glioma cells. Results: The Western blotting results showed that the expression levels of ZEB1 in the glioma U87 cells transfected with shZEB1#1 and shZEB1#2 were significantly lower than that in the cells transfected with shCtrl (P < 0.05 or P < 0.01), and the inhibitory effect of shZEB1#2 on the ZEB1 expression was more obvious, indicating that ZEB1 was stably transfected into the U87 cells. Compared with control group, the expression levels of mesenchymal markers N-cadherin, Vimentin, and MMP-9 in EMT group were significantly increased (P < 0.05 or P < 0.01).Compared with EMT group, the expression levels of the above proteins in ZEB1 silencing group were markedly reduced (P < 0.05 or P < 0.01).The cell migration rate in EMT group was obviously elevated compared with control group (P < 0.01), and the cell migration rate of the glioma U87 cells in ZEB1 silence group was significantly lower than that in EMT group(P < 0.01). Conclusion: Silencing ZEB1 gene expression can inhibit the EMT in the glioma U87 cells and reduce the cell migration abilities, suggesting ZEB1 as an important therapeutic target of invasive glioma.
KEYWORDS: zinc finger E-box binding homeobox     gene silence     glioma U87 cell     epithelial to mesenchymal transition     cell migration    

脑胶质瘤是最常见的原发性恶性肿瘤,具有高度侵袭性生长的病理特性,但其侵袭性生长的机制尚未阐明。上皮-间质转化(epithelial to mesenchymal transition,EMT)的肿瘤细胞呈高迁移性和高侵袭性,对肿瘤的侵袭、转移和复发具有重要作用[1]。本课题组前期工作和其他学者的研究[2-4]已表明:胶质瘤细胞能发生EMT,其可能在胶质瘤侵袭性生长中起重要作用。诱导EMT的转录因子(EMT-inducing transcription factors)通过转录调控EMT相关分子的表达,在诱导和激活EMT中起关键作用[5]。锌指E盒结合同源框(zinc finger E-box binding homeobox, ZEB)是重要诱导EMT转录因子之一,包括ZEB1和ZEB2。目前已有研究[6-7]证明:ZEB1能诱导肺癌、胰腺癌和乳腺癌细胞EMT,并促进肿瘤转移,但ZEB1对胶质瘤细胞EMT的影响尚未见研究报道。本研究使用短发卡RNA(shRNAs)沉默ZEB1基因表达,观察ZEB1对胶质瘤U87细胞EMT的影响,明确ZEB1在促进胶质瘤侵袭性生长中的可能作用。

1 材料与方法 1.1 细胞、主要试剂和仪器

人恶性脑胶质瘤U87细胞(美国ATCC细胞库)。DMEM培养基、胎牛血清和胰酶-EDTA消化液(美国Gibco公司),青霉素和链霉素(美国Sigma公司),抗ZEB1抗体、抗N-钙黏蛋白、抗波形蛋白和抗基质金属蛋白酶9(matrix metalloproteinase-9, MMP-9)抗体(美国Cell Signaling Technology公司),抗β-tubulin抗体(美国Origene公司),TGF-β1(美国PeproTech公司),RIPA裂解液、BCA蛋白测定试剂盒、SDS和上样缓冲液(上海碧云天有限公司),蛋白Marker(美国Thermo公司),转染试剂TransLipid HL(北京全式金生物技术公司)。细胞培养箱和超净工作台(美国Thermo公司),倒置显微镜(日本Olympus公司),电泳仪和转膜仪(美国Bio-Rad公司),台式低速和高速离心机(美国Beckman公司)。

1.2 胶质瘤细胞培养

U87细胞用含10%胎牛血清、1%青霉素和链霉素的DMEM培养基常规培养,每2~3 d更换培养基,每隔3 d按1:2~1:3传代,取对数生长期细胞进行后续实验。

1.3 ZEB1 shRNA干扰质粒的构建及转染

ZEB1 shRNA干扰质粒由上海吉凯基因化学技术有限公司构建。取对数生长期的U87细胞接种于6孔板中,每孔为2×105个细胞,细胞融合约80%时进行质粒转染。按照TransLipid HL转染试剂说明书将ZEB1 shRNAs质粒(分别称shZEB1#1和shZEB1#2)和对照质粒shRNA(shCtrl)转染至U87细胞。质粒为4 μg,转染试剂体积为8~20 μL。转染4~6 h后,更换新的完全培养基,培养48 h后采用Western blotting法检测ZEB1蛋白表达水平,确定ZEB1 shRNAs转染效果。

1.4 Western blotting法鉴定ZEB1干扰效果和检测间质标志物的表达水平

将U87细胞接种在10 cm培养皿(5×105个细胞/皿),37℃、5%CO2培养箱培养,待细胞融合达70%~80%时,换无血清培养基培养12 h,弃掉培养基,离心后收集细胞。加入RIPA裂解液提取蛋白质,采用BCA法测定蛋白质浓度后上样,SDS-PAGE电泳分离蛋白质,湿转至PVDF膜,5%脱脂奶粉室温封闭1 h,分别加入一抗ZEB1、N-钙黏蛋白、波形蛋白、MMP-9和β-tubulin,4℃过夜,洗膜,加入二抗37℃孵育,洗膜,加ECL显色剂,在凝胶成像系统中显影,检测各条带的灰度值,β-tubulin作为内参照。目的蛋白相对表达水平=目的条带灰度值/β-tubulin条带灰度值。

1.5 实验分组

胶质瘤U87细胞分为对照组(胶质瘤U87细胞转染shCtrl)、EMT组(转染shCtrl的U87细胞用10×10-6g·L-1 TGF-β1处理48 h诱导EMT)和ZEB1基因沉默组(转染shZEB1的U87细胞用TGF-β1诱导EMT)。

1.6 细胞划痕法检测细胞迁移率

取上述3组U87细胞接种于6孔培养板(每孔3×105个细胞),采用划痕试验检测和计算各组细胞的迁移率[8]

1.7 统计学分析

采用SPSS 19.0统计软件进行统计学分析。ZEB1、N-钙黏蛋白、波形蛋白和MMP-9蛋白表达水平及细胞迁移率以x±s表示,多组间样本均数比较采用单因素方差分析,组间两两比较采用SNK-q检验。以P<0.05为差异有统计学意义。

2 结果 2.1 沉默ZEB1基因的胶质瘤细胞中ZEB1蛋白表达水平

采用Western blotting法检测转染shCtrl和shZEB1的U87细胞中ZEB1蛋白表达水平,结果显示:2个短发卡RNA(shZEB1#1和shZEB1#2)均能抑制U87细胞中ZEB1蛋白表达水平,转染shZEB1#1和shZEB1#2 U87细胞中ZEB1蛋白表达水平(0.69±0.07和0.49±0.06)均较转染shCtrl的U87细胞(0.92±0.08)明显降低(P < 0.05和P < 0.01),表明ZEB1已稳定转染到U87细胞,成功建立了沉默ZEB1的胶质瘤U87细胞。与转染shZEB1#1的U87细胞(0.69±0.07)比较,转染shZEB1#2的U87细胞中ZEB1蛋白表达水平(0.49±0.06)明显降低(P < 0.05)。表明shZEB1#2对ZEB1表达的抑制效果更明显。在以下实验中使用shZEB1#2。见图 1

图 1 Western blotting法检测各组胶质瘤U87细胞中ZEB1蛋白表达电泳图 Fig. 1 Electrophoregram of expressions of ZEB1 protein in glioma cells in various groups detected by Western blotting method
2.2 各组胶质瘤细胞中N-钙黏蛋白、波形蛋白和MMP-9蛋白表达水平

与对照组比较,EMT组U87细胞中N-钙黏蛋白、波形蛋白和MMP-9蛋白表达水平均明显升高(P < 0.05或P < 0.01);与EMT组比较,ZEB1基因沉默组细胞中N-钙黏蛋白、波形蛋白和MMP-9蛋白表达水平明显降低(P < 0.05或P < 0.01)。见图 2表 1

图 2 各组胶质瘤U87细胞中N-钙黏蛋白、波形蛋白和MMP-9蛋白表达电泳图 Fig. 2 Electrophoregram of expressions of N-cadherin, Vimentin and MMP-9 proteins in glioma U87 cells in various groups
表 1 各组胶质瘤U87细胞中N-钙黏蛋白、波形蛋白和MMP-9蛋白表达水平 Tab. 1 Expression levels of N-cadherin, Vimentin, and MMP-9 proteins in glioma U87 cells in various groups
(n=3, x±s)
Group N-cadherin Vimentin MMP-9
Control 0.97±0.13 0.98±0.16 0.97±0.07
EMT 1.37±0.14* 1.51±0.10** 1.24±0.09*
ZEB1 silence 0.83±0.14△△ 1.25±0.08 0.73±0.10△△
* P < 0.05, ** P < 0.01 vs control group; P < 0.05, △△ P < 0.01 vs EMT group.
2.3 各组U87细胞的迁移率

EMT组细胞迁移率(69%±7%)明显高于对照组(51%±5%, P < 0.01),而ZEB1基因沉默组细胞迁移率(38%±4%)较EMT组明显降低(P < 0.01)。见图 3

A-C: 0 h; D-F: 24 h; A, D: Control group; B, E: EMT group; C, F: ZEB1 silence group 图 3 划痕24 h后各组胶质瘤U87细胞的迁移距离 Fig. 3 Migration distances of glioma U87 cells at 24 h after scratch in various groups
3 讨论

本研究Western blotting法检测结果显示:转染shZEB1#1和shZEB1#2的U87细胞中ZEB1蛋白表达水平均明显降低,与shZEB1#1比较,shZEB1#2对ZEB1表达的抑制效果更为明显,表明ZEB1已稳定转染至U87细胞,成功建立了沉默ZEB1的胶质瘤U87细胞。

EMT是肿瘤细胞侵袭和转移的关键环节。恶性胶质瘤的一个显著特点是向周围组织侵袭性生长,近年来大量研究[9-10]表明:EMT这一病理生理过程在胶质瘤的侵袭性生长中起重要作用。有多种因素能诱导EMT过程,一些转录因子是EMT的重要诱导因子,如ZEB1、ZEB2、Snail、Slug和Twist1等,被称为诱导EMT转录因子或EMT激活剂(EMT-activator)。诱导EMT的转录因子能下调上皮标志蛋白的表达和(或)上调间质标志蛋白的表达,诱导EMT。通过抑制这些EMT诱导转录因子的表达及活性进而抑制并阻止EMT[5],已成为控制肿瘤细胞迁移和转移的策略之一。转录因子ZEB1在肿瘤发生发展中具有多方面作用,最主要的是促进肿瘤细胞EMT[11]。以往研究[7, 12]证明:在胰腺癌模型中使ZEB1失活可以消除侵袭和转移,抑制ZEB1活性可逆转肺癌细胞发生EMT。有研究[13-14]表明:ZEB1对恶性胶质瘤的起动、侵袭和耐药均发挥重要影响,用SHP-2上调ZEB1过表达能增强胶质瘤细胞侵袭和生长。最近对肝癌的研究[15]证明:ZEB1能与波形蛋白启动子中的某个位点结合,并调节波形蛋白基因的转录,这可能是沉默ZEB1基因表达能抑制EMT的分子机制之一。本研究结果显示:应用shZEB1抑制ZEB1基因表达,可明显降低U87细胞中间质标志物N-钙黏蛋白和波形蛋白的表达水平,表明沉默ZEB1能抑制胶质瘤细胞EMT。

基底膜降解是肿瘤侵袭的关键环节。MMP-9是明胶酶的一种,属于侵袭迁移相关蛋白,通过降解Ⅳ型胶原等基膜成分促进肿瘤的侵袭和转移[16]。有研究者[17-18]认为:MMP-9本身就是间质标志物,可以诱导EMT或EMT相关进程。本研究结果显示:应用shZEB1抑制ZEB1基因表达能明显降低胶质瘤细胞中MMP-9蛋白表达水平,提示抑制ZEB1能降低胶质瘤细胞的侵袭能力。增加细胞迁移能力是细胞发生EMT的重要表现之一。本研究结果表明:ZEB1沉默组的细胞迁移率较EMT组明显降低(P < 0.01),表明抑制ZEB1基因表达可以降低U87细胞的迁移能力。

综上所述,本研究结果证明沉默ZEB1基因表达能抑制胶质瘤U87细胞EMT,并降低细胞的迁移能力,提示转录因子ZEB1在促进胶质瘤侵袭性生长中扮演重要角色,可作为高度侵袭性胶质瘤治疗的重要靶标。

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