肿瘤防治研究  2018, Vol. 45 Issue (6): 381-385
本刊由国家卫生和计划生育委员会主管,湖北省卫生厅、中国抗癌协会、湖北省肿瘤医院主办。
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文章信息

Gab2通过调节EMT促进胃癌的侵袭转移
Gab2 Promotes Invasion and Metastasis of Gastric Cancer via Regulating EMT
肿瘤防治研究, 2018, 45(6): 381-385
Cancer Research on Prevention and Treatment, 2018, 45(6): 381-385
http://www.zlfzyj.com/CN/10.3971/j.issn.1000-8578.2018.17.0881
收稿日期: 2017-10-12
修回日期: 2017-12-26
Gab2通过调节EMT促进胃癌的侵袭转移
陈美玲1, 姜迎宵2, 王淑晓1, 孙秀宁3, 张小茜4, 郑书贤5, 张宝刚5, 史立宏1     
1. 261053 潍坊,潍坊医学院,山东省重点实验室应用药理学实验室;
2. 261041 潍坊,潍坊人民医院放射治疗科;
3. 261053 潍坊,潍坊医学院病原微生物实验室;
4. 261042 潍坊,潍坊医学院附属医院胃肠科;
5. 261053 潍坊,潍坊医学院病理学实验室
摘要: 目的 探讨Gab2在胃癌组织中的表达情况及其对胃癌细胞侵袭转移能力的影响与机制。方法 采用免疫组织化学SP法检测胃癌组织中Gab2、E-cadherin、N-cadherin及MMP-9的表达并分析其与淋巴结转移的关系。应用小RNA干扰技术,转染SGC7901细胞株,RT-PCR法检测瞬时转染后Gab2基因表达情况,体外侵袭实验检测细胞转染后侵袭能力的变化,Western blot法检测各蛋白的表达。结果 胃癌组织中Gab2的表达水平与淋巴结转移显著相关(P=0.002),与E-cadherin的表达负相关(r=-0.693, P=0.000),而与N-cadherin和MMP-9的表达水平正相关(r=0.407, P=0.021; r=0.335, P=0.017)。小RNA干扰技术降低Gab2蛋白的表达后SGC7901细胞侵袭转移能力降低,同时E-cadherin表达增多,N-cadherin和MMP-9蛋白表达降低。结论 Gab2可能通过调节EMT在胃癌侵袭转移中发挥重要作用。
关键词: 胃癌     SGC7901     Gab2     上皮间质转化     MMP-9     侵袭    
Gab2 Promotes Invasion and Metastasis of Gastric Cancer via Regulating EMT
CHEN Meiling1, JIANG Yingxiao2, WANG Shuxiao1, SUN Xiuning3, ZHANG Xiaoqian4, ZHENG Shuxian5, ZHANG Baogang5, SHI Lihong1     
1. Shandong Province Key Laboratory of Applied Pharmacology, Weifang Medical University, Weifang 261053, China;
2. Department of Radiotherapy, Weifang People's Hospital, Weifang 261041, China;
3. Department of Pathogeny Microbiology, Weifang Medical University, Weifang 261053, China;
4. Department of Gastroenterology, Affiliated Hospital of Weifang Medical University, Weifang 261042, China;
5. Department of Pathology, Weifang Medical University, Weifang 261053, China
Corresponding author: SHI Lihong, E-mail: shilih@163.com.
Abstract: Objective To investigate the expression of Grb2 binding protein-2(Gab2) in gastric cancers and its significance and mechanism in the invasiveness and metastasis of gastric cancer. Methods Immunohistochemical method was used to detect the expression of Gab2, E-cadherin, N-cadherin and MMP-9 in gastric cancer tissues. The relationship between Gab2 expression and lymphatic metastasis was analysed. SiRNA plasmid targeting Gab2 and empty vector plasmid were transfected into SGC7901 cells and named siGab2/SGC7901 and NC/SGC7901 cells respectively. RT-PCR method was applied to analyze mRNA expression of Gab2 in siGab2/SGC7901 and NC/SGC7901 cells. In vitro matrigel invasion assay was used to detect the invasiveness of siGab2/SGC7901 and SGC7901 cells. Western blot was applied to analyze protein expression. Results Gab2 expression in gastric cancer tissues was related with lymphatic metastasis significantly(P=0.002), E-cadherin expression level negatively (r=-0.693, P=0.000), and N-cadherin and MMP-9 levels positively (r=0.407, P=0.021; r=0.335, P=0.017). After microRNA interference, the mRNA and protein expressions of Gab2 in siGab2/SGC7901 cells were decreased obviously, moreover, the quantity of gastric cancer cells which invaded and penetrated matrigel membrane was decreased. Western blot showed that the expressions of N-cadherin and MMP-9 were decreased and E-cadherin expression was increased in siGab2/SGC7901 cells. Conclusion Gab2 plays a key role in the invasiveness and metastasis of gastric cancer by regulating EMT.
Key words: Gastric cancer     SGC7901     Gab2     EMT     MMP-9     Invasiveness    
0 引言

胃癌是我国常见的恶性肿瘤之一,其导致患者死亡的主要原因是原发灶的浸润和转移。近来的研究发现Grb2协同结合蛋白2(Grb2 binding protein-2, Gab2)可能是一个重要的肿瘤转移调控蛋白,其高表达与某些肿瘤的恶性程度、侵袭转移能力密切相关[1-3]。但到目前为止,Gab2在胃癌组织中的表达及其对胃癌侵袭迁移的影响尚未见报道。本研究应用免疫组织化学技术检测胃癌组织中Gab2的表达,并通过基因干扰技术抑制胃癌细胞株SGC7901细胞Gab2的表达,观察Gab2对SGC7901细胞体外侵袭转移能力的影响,并初步探讨其可能的机制。

1 资料与方法 1.1 资料

1.1.1 病例资料

收集潍坊医学院病理学教研室2013年3月1日至2016年11月30日有完整病理资料的胃癌蜡块标本50例,病理诊断均为腺癌,其中高分化5例,中分化12例,低分化33例;侵犯肌层36例,侵犯浆膜层14例;有淋巴结转移39例,未发生转移11例;Ⅰ期5例,Ⅱ期21例,Ⅲ期20例,Ⅳ期4例。患者年龄34~78岁,中位年龄56岁,其中男36例,女14例。所有患者术前均未接受任何抗肿瘤治疗。

1.1.2 主要试剂

细胞培养产品购自美国Hyclone公司;Lipofectamin2000购自上海Invitrogen公司;细胞培养板和Transwell小室购自上海玉博生物科技有限公司;Matrigel膜基质购自北京威格拉斯生物技术有限公司;0.1%Fibronectin、HEPES和BSA购自美国Sigma公司;RT-PCR引物与试剂盒购自上海生工公司;Gab2、E-cadherin、N-cadherin、MMP-9一抗购自美国Santa Cruz公司;二抗及免疫组织化学试剂盒购自北京中杉金桥公司。

1.2 方法

1.2.1 免疫组织化学

采用免疫组织化学SP法,操作方法按试剂说明书,胃癌组织免疫组织化学染色在显微镜下观察,Gab2和MMP-9以胞质出现浅黄到棕色颗粒沉淀为阳性,E-cadherin及N-cadherin以胞膜呈现浅黄到棕色为阳性。高倍镜(×400)下每张切片至少选择5个随机视野,随机计数500个细胞,阳性细胞占同类计数细胞的百分比为阳性细胞率。阳性结果的判定根据阳性细胞率及显色深浅分级:无细胞显色为0分,< 10%细胞显色为1分,10%~50%细胞显色为2分,> 50%细胞显色为3分。显色深浅:不显色或显色不清为0分,浅黄色为1分,黄棕色为2分,棕色为3分。两项乘积≥6分为高表达,≤4分为低表达。

1.2.2 细胞培养

人胃癌细胞株SGC7901购自美国ATCC细胞库。SGC7901细胞常规培养于10%胎牛血清中,加入终浓度各为100 u/ml的青霉素和0.1 mg/ml的链霉素,置37℃、5%CO2培养箱中传代培养。采用对数生长期的细胞进行实验。当细胞密度达到80%时分别转染插入Gab2目标片段5'-GTGAGAACGATGAGAAATA-3'的小RNA干扰质粒和空白对照序列的小RNA干扰质粒,转染步骤参照转染试剂说明书。转染细胞株分别命名为实验组siGab2/SGC7901细胞和对照组NC/SGC7901细胞。

1.2.3 MTT细胞增殖实验

取对数生长期细胞,以1×103个/孔接种于96孔板,培养24 h,待其贴壁后用无血清培养液洗涤3次,继续培养12 h后开始实验。将实验组和对照组细胞分别培养1、2、3、4、5 d后加入MTT溶液20 μl,37℃孵育4 h,弃去培养液,加入二甲基亚砜(DMSO),振荡10 min后在570 nm波长处测定吸光度值,实验重复3次。

1.2.4 RT-PCR实验

用TRIzol抽提细胞总RNA,内参β-actin扩增片段长度为491 bp,Gab2扩增片段长度为240 bp。Gab2引物:上游:5'-CTGAGACTGATAACGAGGAT-3',下游:5'-GAGGTGTTTCTGCTTGAC-3';β-actin引物:上游:5'-ATGTTTG AGACCTTCAACAC-3',下游:5'-CACGTCACACTTCATGATGG-3'。PCR产物在2%琼脂糖进行凝胶电泳,于Bio-Rad凝胶成像仪下观察并照相,用Quantity One进行定量分析。

1.2.5 体外侵袭实验

应用8 μm滤膜Transwell小室,用前铺上Matrigel膜基质并干燥,将NC/SGC7901和siGab2/SGC7901细胞悬液各200 μl(5×105cells/ml)加入Boyden小室上室。下室加入300 μl BM(RPMI 1640培养液,0.1%BSA,25 mmol/L HEPES)。5%CO2、37℃培养24 h。然后取出培养板弃去Boyden小室内培养液,用棉签擦净上室面的人工基底胶和细胞,下室面用甲醇固定10 min,苏木精对比染色,置400倍光学显微镜下观察,计数小室下室面的细胞数即为穿透人工基膜的细胞数,计数5个高倍镜视野。每个实验重复3次。

1.2.6 Western blot实验

将转染后的siGab2/SGC7901和NC/SGC7901细胞培养72 h后提取蛋白,制备SDS-PAGE凝胶,蛋白质变性后电泳,转膜、封闭,分别滴加Gab2、E-cadherin、N-cadherin及MMP-9一抗、二抗孵育后显影。以目的蛋白条带的灰度值与内参照β-actin蛋白条带的灰度值的比值表示蛋白的相对表达量,实验重复3次。

1.3 统计学方法

运用SPSS13.0做统计学处理。对所有定量资料数据结果用(x±s)表示,进行χ2检验、Spearman相关分析和两独立样本的t检验。P < 0.05为差异有统计学意义。

2 结果 2.1 胃癌组织中Gab2、E-cadherin、N-cadherin和MMP-9蛋白的表达

Gab2在50例胃癌组织中的阳性表达率为100%,而且72%胃癌组织中Gab2高表达。癌旁非肿瘤组织的Gab2阳性表达率仅为14%,且全部为低表达。Gab2表达与病理分期无显著相关性(P=0.090),与淋巴结转移情况显著相关,(P=0.002),见表 1。四种蛋白在胃癌中的表达有相关性,Gab2高表达时,N-cadherin与MMP-9在胃癌中也呈高表达,E-cadherin则低表达;Gab2低表达时,N-cadherin与MMP-9也呈低表达,E-cadherin则高表达,见表 2图 1

表 1 胃癌组织中Gab2的表达与病理分期和淋巴结转移的关系 Table 1 Correlation of Gab2 binding protein-2(Gab2) expression with lymph node metastasis, pathological stage in gastric cancer tissues

表 2 胃癌组织中Gab2与E-钙黏蛋白、N-钙黏蛋白及基质金属蛋白酶-9之间的关系 Table 2 Relationship of Gab2 expression with E-cadherin, N-cadherin and MMP-9 in gastric cancer tissues

There were high expression of Gab2, MMP-9, N-cadherin and low expression of E-cadherin in gastric cancer tissues with lymph node metastasis, while low expression of Gab2, MMP-9, N-cadherin and high expression of E-cadherin in gastric cancer tissues without lymph node metastasis (IHC×200) 图 1 Gab2、MMP-9、E-cadherin和N-cadherin在胃癌组织中的表达与淋巴结转移的关系 Figure 1 Correlation of Gab2, MMP-9, E-cadherin and N-cadherin expression with lymph node metastasis in gastric cancer tissues
2.2 SGC7901细胞中Gab2 mRNA与蛋白的表达

RT-PCR结果显示siRNA干扰明显降低了siGab2/SGC7901细胞中Gab2 mRNA及蛋白的表达,与对照组NC/SGC7901细胞比较差异有统计学意义(P=0.003, P < 0.01),见图 2,表明通过基因沉默获得了Gab2低表达的细胞,为后续实验奠定了基础。

RT-PCR and Western blot results showed that after microRNA interference, the mRNA and protein expressions of Gab2 in siGab2/SGC7901 cells were decreased obviously, while no significant difference was observed in SGC7901 or NC/SGC7901 cells 图 2 SGC7901、NC/SGC7901和siGab2/SGC7901细胞中Gab2 mRNA与蛋白的表达 Figure 2 Expression of Gab2 mRNA and protein in SGC7901, NC/SGC7901 and siGab2/SGC7901 cells
2.3 细胞增殖实验

MTT结果显示,小RNA干扰后siRNA/SGC7901细胞增殖显著减慢,OD值与对照组相比差异有统计学意义(P=0.048, P < 0.05)。说明Gab2表达下降后细胞增殖能力明显下降,见图 3

图 3 Gab2表达降低对SGC7901细胞增殖的影响 Figure 3 Effect of decreased Gab2 expression on proliferation of SGC7901 cells
2.4 体外侵袭实验

siGab2/SGC7901穿过8 μm微孔滤膜的细胞数与NC/SGC7901细胞数目比较明显减少,差异有统计学意义(P=0.005, P < 0.01),说明Gab2表达降低后细胞的侵袭能力明显下降,见图 4

In vitro matrigel invasion assay results showed that reduced expression of Gab2 could inhibit the invasion of SGC7901 cells and the quantity of gastric cancer siGab2/SGC7901cells which invaded and penetrated matrigel membrane was decreased; *: P < 0.01 图 4 Gab2表达降低对SGC7901细胞侵袭能力的影响 Figure 4 Effect of decreased Gab2 expression on invasiveness of SGC7901 cells
2.5 siGab2/SGC7901细胞中E-cadherin、N-cadherin、MMP-9和Snail蛋白的表达

为了进一步探究Gab2蛋白影响胃癌细胞侵袭性的机制,应用Western blot法检测E-cadherin、N-cadherin、MMP-9和Snail蛋白的表达。结果显示siGab2/SGC7901细胞中E-cadherin蛋白表达上调,N-cadherin、Snail和MMP-9蛋白表达下调,与NC/SGC7901细胞比较差异有统计学意义(P < 0.01),见图 5

Western blot showed that the expressions of N-cadherin and MMP-9 and Snail were decreased while E-cadherin expression was increased in siGab2/SGC7901 cells 图 5 Gab2表达降低对SGC7901细胞E-cadherin、N-cadherin、MMP-9与Snail蛋白表达的影响 Figure 5 Effect of decreased Gab2 expression on expression of E-cadherin, N-cadherin, MMP-9 and Snail in SGC7901 cells
3 讨论

胃癌的浸润和转移是导致患者死亡的主要原因,从分子水平深入研究其浸润转移的机制,具有重要意义[4]。作为一类连接蛋白,生长因子受体结合蛋白2(Grb2)的相关结合蛋白家族参与了细胞内多种信号转导通路,是酪氨酸激酶(PTKs)激活的下游信号转导通路的关键分子。Gab2是这个家族的重要成员,接受胞外多种因子刺激后被PTKs磷酸化激活,招募富含SH2结构域的信号转运分子,活化下游PI3K/AKT和SHP2/Ras/ERK等一系列信号转导途径,在细胞增殖、分化及迁移等生理过程中发挥重要作用[5-6]。近年研究发现,Gab2在乳腺癌、卵巢癌、肺癌、脑胶质细胞瘤等恶性肿瘤中高表达,并参与调控肿瘤的发生及转移[7-11]。本研究结果显示,Gab2在胃癌组织中的表达较癌旁组织明显升高,并且与淋巴结转移显著相关。有淋巴结转移的胃癌组织中Gab2高表达,而无淋巴结转移的胃癌组织中Gab2表达较低。体外细胞实验也发现特异性siRNA沉默Gab2后,胃癌SGC7901细胞迁移侵袭能力明显降低,与Lee等的结果一致[12],进一步证实了Gab2参与调节肿瘤的迁移侵袭过程,提示Gab2在胃癌的侵袭转移中发挥重要作用。

肿瘤细胞从原发部位脱落是肿瘤浸润和转移的第一步,这与细胞黏附性减低有关,而上皮间质转化(epithelial-mesenchymal transition, EMT)是肿瘤细胞黏附性降低的重要原因。有研究表明,Snail的表达诱导了EMT过程,增强了肿瘤细胞的运动和侵袭能力[13]。此外,E-cadherin是上皮细胞表型的标记分子,而N-cadherin是间质细胞表型的标记分子,E-cadherin表达降低及N-cadherin表达增高均可以增强肿瘤细胞的侵袭转移能力[14]。本研究结果表明,在有淋巴结转移的胃癌中E-cadherin低表达或缺失,而无淋巴结转移的胃癌组织中表达较高,与Gab2的表达呈负相关。恰恰相反,N-cadherin在有淋巴结转移的胃癌中高表达,在无淋巴结转移的胃癌组织中则表达较低,与Gab2的表达呈正相关,提示Gab2可能通过调控EMT在胃癌的浸润和转移过程中发挥重要作用。Ding等的研究表明Gab2的过表达能够促进EMT,抑制肿瘤细胞E-cadherin的表达[14-15],与本研究的结果相一致。

另外,MMP-9作为基质金属蛋白酶家族的重要成员之一,与肿瘤侵袭、转移关系最为密切。有研究显示,PI3K/Akt信号通路能够被酪氨酸磷酸化的Gab2激活,活化的PI3K/Akt信号通路会抑制E-cadherin表达,促进MMP-9的表达,而MMP-9对EMT有辅助作用,进一步增强肿瘤细胞的侵袭转移能力[14]。本研究结果表明,在有淋巴结转移的胃癌组织中,MMP-9高表达,而无淋巴结转移的胃癌组织中MMP-9表达较低,与Gab2的表达呈正相关,提示MMP-9高表达后胃癌的侵袭能力增强。为进一步探究Gab2对胃癌侵袭转移的作用机制,本组实验检测了siRNA沉默Gab2后SGC7901细胞中MMP-9蛋白和转录因子Snail的表达水平。结果显示MMP-9和Snail的表达在Gab2沉默的SGC7901细胞中显著减少,提示Gab2可能通过促进上皮间质转化,降低E-cadherin的表达,增高MMP-9和Snail的表达来促进细胞的侵袭和转移。

综上所述,本研究结果提示Gab2可能通过调控EMT在胃癌的侵袭转移中发挥重要作用,有可能成为胃癌治疗的一个潜在靶点。

参考文献
[1] Ding CB, Yu WN, Feng JH, et al. Structure and function of Gab2 and its role in cancer(Review)[J]. Mol Med Rep, 2015, 12(3): 4007–14. DOI:10.3892/mmr.2015.3951
[2] Luo LY, Hahn WC. Oncogenic Signaling Adaptor Proteins[J]. J Genet Genomics, 2015, 42(10): 521–9. DOI:10.1016/j.jgg.2015.09.001
[3] Ma J, Yu J, Liu J, et al. MicroRNA-302a targets GAB2 to suppress cell proliferation, migration and invasion of glioma[J]. Oncol Rep, 2017, 37(2): 1159–67. DOI:10.3892/or.2016.5320
[4] Özer İ, Bostancı EB, Ulaş M, et al. Changing Trends in Gastric Cancer Surgery[J]. Balkan Med J, 2017, 34(1): 10–20. DOI:10.4274/balkanmedj
[5] Adams SJ, Aydin IT, Celebi JT. GAB2-a Scaffolding Protein in Cancer[J]. Mol Cancer Res, 2012, 10(10): 1265–70. DOI:10.1158/1541-7786.MCR-12-0352
[6] Vaughan TY, Verma S, Bunting KD. Gab2-associated binding(Gab) proteins in hematopoitic and immune cell biology[J]. Am J Blood Res, 2011, 1(2): 130–4.
[7] Xu LJ, Wang YC, Lan HW, et al. Grb2-associated binder-2 gene promotes migration of non-small cell lung cancer cells via Akt signaling pathway[J]. Am J Transl Res, 2016, 8(2): 1208–17.
[8] Ding C, Luo J, Fan X, et al. Elevated Gab2 induces tumor growth and angiogenesis in colorectal cancer through upregulating VEGF levels[J]. J Exp Clin Cancer Res, 2017, 36(1): 56. DOI:10.1186/s13046-017-0524-2
[9] Shi L, Sun X, Zhang J, et al. Gab2 expression in glioma and its implications for tumor invasion[J]. 2013, 52(8): 1739-50. http://www.ncbi.nlm.nih.gov/pubmed/23231021
[10] Zhang X, Dong Z, Zhang Z, et al. Critical Role for GAB2 in Neuroblastoma Pathogenesis Through the Promotion of SHP2/MYCN Cooperation[J]. Cell Rep, 2017, 18(12): 2932–42. DOI:10.1016/j.celrep.2017.02.065
[11] Duckworth C, Zhang L, Carroll SL, et al. Overexpression of GAB2 in ovarian cancer cells promotes tumor growth and angiogenesis by upregulating chemokine expression[J]. Oncogene, 2016, 35(31): 4036–47. DOI:10.1038/onc.2015.472
[12] Lee SH, Jeong EG, Nam SW, et al. Increased expression of Gab2, a scaffolding adaptor of the tyrosine kinase signalling, in gastric carcinomas[J]. Pathology, 2007, 39(3): 326–9.
[13] Wieczorek K, Wiktorska M, Sacewiczhofman I, et al. Filamin A upregulation correlates with Snail-induced epithelial to mesenchymal transition (EMT) and cell adhesion but its inhibition increases the migration of colon adenocarcinoma HT29 cells[J]. Exp Cell Res, 2017, 359(1): 163–70. DOI:10.1016/j.yexcr.2017.07.035
[14] Ding C, Luo J, Li L, et al. Gab2 facilitates epithelial-to-mesenchymal transition via the MEK/ERK/MMP signaling in colorectal cancer[J]. J Exp Clin Cancer Res, 2016, 35: 5. DOI:10.1186/s13046-015-0280-0
[15] Yip WK, Seow HF. Activation of phosphatidylinositol 3-kinase/Akt signaling by EGF downregulates membranous E-cadherin and b-catenin and enhances invasion in nasopharyngeal carcinoma cells[J]. Cancer Lett, 2012, 318(2): 162–72. DOI:10.1016/j.canlet.2011.12.018