吉林大学学报(医学版)  2020, Vol. 46 Issue (04): 751-758     DOI: 10.13481/j.1671-587x.20200414

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陈艳, 潘殿柱, 刘忠, 马艳梅, 张岚
CHEN Yan, PAN Dianzhu, LIU Zhong, MA Yanmei, ZHANG Lan
沉默重组蛋白2对NCI-H1688细胞的抑制作用及其Wnt/β连环蛋白信号通路机制
Inhibitory effect of sileneing Frat2 on NCI-H1688 cells and its Wnt/β catenin signaling pathway mechanism
吉林大学学报(医学版), 2020, 46(04): 751-758
Journal of Jilin University (Medicine Edition), 2020, 46(04): 751-758
10.13481/j.1671-587x.20200414

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收稿日期: 2019-10-15
沉默重组蛋白2对NCI-H1688细胞的抑制作用及其Wnt/β连环蛋白信号通路机制
陈艳 , 潘殿柱 , 刘忠 , 马艳梅 , 张岚     
锦州医科大学附属第一医院呼吸科, 辽宁 锦州 121000
[摘要]: 目的 探讨T细胞淋巴瘤常见重排蛋白2(Frat2)通过Wnt/β连环蛋白(β-catenin)信号通路对小细胞肺癌NCI-H1688细胞增殖的影响,阐明其可能机制。方法 选取生长状态良好的人小细胞肺癌NCI-H1688细胞和正常支气管上皮样细胞HBE细胞,采用Western blotting法和逆转录实时荧光定量-聚合酶链反应(Real-Time RT-qPCR)法分别检测NCI-H1688细胞和HBE细胞中Frat2蛋白及mRNA表达水平。NCI-H1688细胞随机分为空白对照组、阴性对照组、Frat2-siRNA组和Frat2-siRNA+XAV组。空白对照组细胞不转染,阴性对照组细胞转染阴性对照慢病毒,Frat2-siRNA组转染Frat2-siRNA慢病毒,Frat2-siRNA+XAV组转染Frat2-siRNA慢病毒并同时加入4 μmol·L-1 Wnt信号通路抑制剂XAV939。采用Western blotting法和Real-Time RT-qPCR法分别检测转染后各组细胞中Frat2蛋白和mRNA表达水平,采用MTT法检测各组细胞增殖活性,采用流式细胞术检测不同细胞周期细胞百分率,采用Western blotting法检测细胞中增殖细胞核抗原(PCNA)、c-myc、细胞周期蛋白D1(Cyclin D1)、β-catenin和磷酸化糖原合成酶激酶3(pGSK-3β)蛋白表达水平。结果 与HBE细胞比较,NCI-H1688细胞中Frat2蛋白和mRNA表达水平明显升高(P<0.01)。与空白对照组和阴性对照组比较,Frat2-siRNA组NCI-H1688细胞中Frat2蛋白和mRNA表达水平明显升高(P<0.05);空白对照组与阴性对照组NCI-H1688细胞中Frat2蛋白和mRNA表达水平比较差异无统计学意义(P>0.05)。与空白对照组和阴性对照组比较,Frat2-siRNA组细胞增殖活性降低(P<0.05),G0/G1期细胞百分率升高(P<0.05),S期和G2/M期细胞百分率降低(P<0.05),PCNA、c-myc、Cyclin D1、β-catenin和pGSK-3β蛋白表达水平降低(P<0.05);与Frat2-siRNA组比较,Frat2-siRNA+XAV组细胞增殖活性降低(P<0.05),G0/G1期细胞百分率升高(P<0.05),S期和G2/M期细胞百分率降低(P<0.05),PCNA、c-myc、Cyclin D1、β-catenin和pGSK-3β蛋白表达水平降低(P<0.05);空白对照组与阴性对照组上述各指标比较差异无统计学意义(P>0.05)。结论 沉默Frat2可抑制小细胞肺癌细胞增殖,其机制可能与抑制Wnt/β-catenin信号通路有关。
关键词: 重组蛋白2    Wnt/β连环蛋白信号通路    小细胞肺癌    细胞增殖    增殖细胞核抗原    细胞周期蛋白D1    糖原合成酶激酶3    
Inhibitory effect of sileneing Frat2 on NCI-H1688 cells and its Wnt/β catenin signaling pathway mechanism
CHEN Yan , PAN Dianzhu , LIU Zhong , MA Yanmei , ZHANG Lan     
Department of Respiratory Medicine, First Affiliated Hospital, Jinzhou Medical University, Jinzhou 121000, China
[ABSTRACT]: Objective To investigate the effect of frequently rearranged in advanced T-cell lymphomas 2 (Frat2) on the proliferation of small cell lung cancer NCI-H1688 cells via Wnt/β-catenin signaling pathway, and to elucidate its possible mechanism. Methods The human small cell lung cancer NCI-H1688 cells with good growth status and the normal bronchial epithelial-like cells HBE were selected; Western blotting method and Real-Time RT-qPCR were used to detect the expression levels of Frat2 mRNA and protein in the NCI-H1688 cells and the HBE cells.The NCI-H1688 cells were randomly divided into blank control group, negative control group, Frat2-siRNA group and Frat2-siRNA+XAV group.The cells in blank control group were not transfected.The cells in negative control group were transfected with negative control lentivirus, the cells in Frat2-siRNA group were transfected with Frat2-siRNA lentivirus and the cells in Frat2-siRNA+XAV group were transfected with the Frat2-siRNA lentivirus and treated with 4 μmol·L-1 of Wnt signaling pathway inhibitor XAV939.The expression levels of Frat2 protein and mRNA in the cells in various groups were determined by Western blotting method and Real-Time RT-qPCR method.The proliferation activities of the cells in various groups were determined by MTT method.The percentages of cells in different cell cycles were measured by flow cytometry.The expression levels of Frat2, proliferating cell nuclear antigen (PCNA), c-myc, cyclin D1, β-catenin and phosphorylated glycogen synthase kinase 3 (pGSK-3β) proteins in the cells were determined by Western blotting method. Results Compared with the normal bronchial epithelial-like cells HBE, the levels of Frat2 protein and mRNA in the NCI-H1688 cells were elevated (P < 0.01).Compared with blank control group and negative control group, the expression levels of protein and Frat2 mRNA in Frat2-siRNA group were increased (P < 0.05).There were no significant difference in the expression levels of Frat2 protein and mRNA in the NCI-H1688 cells between blank control group and negative control group (P > 0.05).Compared with blank control group and negative control group, the proliferation activity of the cells in Frat2-siRNA group was decreased (P < 0.05), the percentage of cells in G0/G1 phase was increased (P < 0.05), the percentages of cells in S phase and G2/M phase were decreased (P < 0.05), and the expression levels of PCNA, c-myc, Cyclin D1, β-catenin and pGSK-3β proteins were decreased (P < 0.05).Compared with Frat2-siRNA group, the proliferation activity of cells in Frat2 mRNA+XAV group was decreased(P < 0.05), the percentage of cells in G0/G1 phase was increased (P < 0.05), the percentages of cells in S phase and G2/M phase were decreased (P < 0.05), and the expression levels of PCNA, c-myc, Cyclin D1, β-catenin and pGSK-3β proteins were decreased (P < 0.05).There were no significant differences in the indexes mentioned above between blank control group and negative control group (P > 0.05). Conclusion Silencing Frat2 can inhibit the proliferation of small cell lung cancer cells, and its mechanism may be related to the inhibition of Wnt/β-catenin signaling pathway.
KEYWORDS: frequently rearranged in advanced T-cell lymphomas 2    Wnt/β-catenin signaling pathway    small cell lung cancer    proliferation    proliferating cell nuclear antigen    cyclin D1    glycogen synthase kinase 3    

T细胞淋巴瘤常见重排蛋白(frequently rearranged in advanced T-cell lymphomas,Frat)最早作为T细胞淋巴瘤原癌基因被发现,后来证实Frat为Wnt信号通路的重要组成部分。Frat包括Frat1和Frat2,研究[1-2]证实:Frat1通过Wnt信号通路在多种恶性肿瘤中发挥作用。张勇等[3]研究发现:Frat1在非小细胞肺癌组织中异常表达,其表达水平与肺癌细胞的侵袭和迁移等关系密切。Frat2也是Wnt信号通路的正向调节因子,但Frat2在肺癌中的作用尚不清楚。Wnt信号通路在小细胞肺癌细胞的增殖中发挥重要作用[4-5],而Frat2主要通过Wnt信号通路发挥作用,故本研究对NCI-H1688细胞中Frat2的表达及沉默Frat2对NCI-H1688细胞增殖及Wnt信号通路的影响进行研究,探讨Frat2对小细胞肺癌的可能作用机制。XAV939为Wnt/β连环蛋白(β-catenin)信号通路抑制剂,可抑制Wnt/β-catenin的调节转录,本研究同时对NCI-H1688细胞给予XAV939处理,进一步验证Frat2对小细胞肺癌的作用是否与Wnt/β-catenin信号通路有关。

1 材料与方法 1.1 细胞、主要试剂和仪器

人小细胞肺癌NCI-H1688细胞和正常支气管上皮样细胞HBE细胞(中国科学院上海细胞库)。Frat2-siRNA慢病毒及阴性对照慢病毒(上海吉凯基因构建制备),逆转录(reverse transcription,RT)试剂盒、TRIzol试剂、聚合酶链反应(polymerase chain reaction,PCR)试剂盒和ECL化学发光试剂盒(美国BPB公司),Wnt信号通路抑制剂XAV939、胰蛋白酶、MTT试剂和DMEM培养基(美国Sigma公司),鼠抗人Frat2单克隆抗体(货号:SC-100437)、鼠抗人增殖细胞核抗原(proliferating cell nuclear antigen,PCNA)单克隆抗体(货号:SC-103214)、鼠抗人c-myc单克隆抗体(货号:SC-100801)、鼠抗人细胞周期蛋白D1(Cyclin D1)单克隆抗体(货号:SC-100025)、鼠抗人β-catenin单克隆抗体(货号:SC-100183)和鼠抗人磷酸化糖原合成酶激酶3(phosphorylated glycogen synthase kinase 3,pGSK-3β)单克隆抗体(货号:SC-10427)(美国Invitrogen公司)。PCR扩增仪(美国Gibco公司),流式细胞仪和酶标仪(美国Bio-Rad公司)。

1.2 Western blotting法检测NCI-H1688细胞和HBE细胞中Frat2蛋白表达水平

取生长良好的NCI-H1688细胞和HBE细胞,加入蛋白裂解液裂解后,12 000 r·min-1离心10 min,取上清液采用BCA法测定蛋白浓度,在SDS-PAGE凝胶中加入30 μg蛋白样品,电泳、转膜,加入封闭液封闭2h,加入一抗:兔抗人Frat2单克隆抗体(1:200)过夜孵育,加入含辣根过氧化物酶标记的二抗孵育1h,ECL发光。以β-actin为内参,实验重复7次,采用凝胶电泳成像仪采集图像,Quantity One软件分析蛋白条带灰度值。Frat2蛋白表达水平以Frat2条带灰度值/β-actin条带灰度值比值表示。

1.3 逆转录实时荧光定量聚合酶链反应(Real-Time RT-qPCR)法检测NCI-H1688细胞和HBE细胞中Frat2 mRNA表达水平

取生长良好的NCI-H1688细胞和HBE细胞加入TRIzol裂解液充分裂解,加入氯仿震荡15 s、静止3 min,2 000 r·min-1离心10 min,吸取上层水相溶液、异丙醇沉淀,乙醇洗涤,提取总RNA,逆转录为cDNA,进行Real-Time RT-qPCR,以GAPDH为内参。反应条件:95℃预变性60 s,60℃变性30 s,60℃退火30 s,共42个循环。引物序列:Frat2,上游5′-GTGGCTTCTCACCGAATCCAG-3′,下游5′-AGTGACTGAGTCCGGTCCG-3′,扩增长度325 bp; GAPDH,上游5′-GAAGTGAAGGTCGGAGTCA-3′,下游5′-TTCACACCCATGACGAACAT-3′,扩增长度402 bp。每组实验重复7次,以2-ΔΔCt法计算Frat2 mRNA表达水平。

1.4 细胞分组和慢病毒转染

将NCI-H1688细胞随机分为空白对照组、阴性对照组、Frat2-siRNA组和Frat2-siRNA+XAV组。空白对照组细胞不转染,阴性对照组细胞转染阴性对照慢病毒,Frat2-siRNA组细胞转染Frat2-siRNA慢病毒,Frat2-siRNA+XAV组细胞转染Frat2-siRNA慢病毒并同时加入4μmol·L-1的Wnt信号通路抑制剂XAV939处理[5]。具体步骤:将各组NCI-H1688细胞洗涤,以5×104个/孔接种至6孔板中,吸出培养液上清后加入适量病毒液,使感染复数(MOI)为20,培养12 h,显微镜下观察各组细胞生长情况,转染4 d后检测转染效率,转染效率高于90%时用于实验。

1.5 转染效果测定

取上述稳定转染的各组NCI-H1688细胞,采用Western blotting法和Real-Time RT-qPCR法测定各组NCI-H1688细胞中Frat2蛋白和mRNA表达水平,具体步骤同“1.2”和“1.3”。

1.6 MTT法检测各组NCI-H1688细胞增殖活性

将上述各组转染后细胞接种到96孔板中,每孔1×104个细胞,培养24、48和72 h时分别在每孔细胞中加入20 μL MTT溶液,继续培养4 h,吸取培养液上清液,加入150 μL二甲基亚砜,震荡反应10 min,用酶联免疫检测仪测定490 nm波长处吸光度(A)值,代表细胞增殖活性,每组实验重复7次。

1.7 流式细胞术检测各组不同细胞周期细胞百分率

取上述转染后各组NCI-H1688细胞,2 000 r·min-1离心10 min,弃去上清液,加入PBS液,调整细胞浓度为5×105 mL-1,加入乙醇固定12 h,加入PBS液重悬细胞,加入碘化丙啶染色液孵育30 min,采用流式细胞仪检测各组不同细胞周期NCI-H1688细胞百分率,每组实验重复7次。

1.8 Western blotting法检测各组NCI-H1688细胞中PCNA、c-myc、Cyclin D1、β-catenin和pGSK-3β蛋白表达水平

取各组转染后NCI-H1688细胞,采用Western blotting法测定各蛋白浓度,一抗分别为兔抗人PCNA单克隆抗体、兔抗人c-myc单克隆抗体、兔抗人Cyclin D1单克隆抗体、兔抗人β-catenin单克隆抗体和兔抗人pGSK-3β单克隆抗体。具体方法同“1.2”。

1.9 统计学分析

采用SPSS20.0统计软件进行统计学分析。各组细胞中Frat2蛋白和mRNA表达水平、细胞增殖活性、不同细胞周期细胞百分率和细胞中PCNA、c-myc、Cyclin D1、β-catenin及pGSK-3β蛋白表达水平均符合正态分布,以x±s表示,2组间样本均数比较采用t检验,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LSD检验。以P<0.05为差异有统计学意义。

2 结果 2.1 NCI-H1688细胞和HBE细胞中Frat2蛋白和mRNA表达水平

NCI-H1688细胞中Frat2蛋白和mRNA表达水平明显高于HBE细胞(P<0.01)。见表 1图 1

表 1 NCI-H1688细胞和HBE细胞中Frat2蛋白和mRNA表达水平 Tab. 1 Expression levels of Frat2 protein and mRNA in NCI-H1688 cells and HBE cells 
(n=7, x±s)
Cell Frat2 protein Frat2 mRNA
NCI-H1688 0.37±0.06 2.34±0.32
HBE 0.12±0.03 1.00±0.11
t 9.860 10.477
P <0.01 <0.01
Lane 1:NCI-H1688 cells; Lane 2:HBE cells. 图 1 Western blotting法检测NCI-H1688细胞和HBE细胞中Frat2蛋白表达电泳图 Fig. 1 Electrophoregram of expressions of Frat2 protein in NCI-H1688 and HBE cells detected by Western blotting method
2.2 Frat2-siRNA转染效果

与空白对照组和阴性对照组比较,Frat2-siRNA组NCI-H1688细胞中Frat2蛋白和mRNA表达水平明显升高(P<0.05);与空白对照组比较,阴性对照组NCI-H1688细胞中Frat2蛋白和mRNA表达水平差异无统计学意义(P>0.05)。见表 2图 2

表 2 各组NCI-H1688细胞中Frat2蛋白和mRNA表达水平 Tab. 2 Expression levels of Frat2 protein and mRNA in NCI-H1688 cells in various groups 
(n=7, x±s)
Group Frat2 protein Frat2 mRNA
Blank control 0.43±0.08 1.00±0.11
Negative control 0.39±0.09 0.98±0.09
Frat2-siRNA 0.16±0.07*△ 0.47±0.12*△
F 22.985 54.766
P <0.01 <0.01
*P<0.05 compared with blank control group;P<0.05 compared with negative control group.
Lane 1:Blank control group; Lane 2:Negative control group; Lane 3:Frat2-siRNA group. 图 2 Western blotting法检测各组NCI-H1688细胞中Frat2蛋白表达电泳图 Fig. 2 Electrophoregram of expressions of Frat2 protein in NCI-H1688 cells in various groups detected by Western blotting method
2.3 各组NCI-H1688细胞增殖活性

细胞培养24 h时,各组细胞增殖活性比较差异无统计学意义(P>0.05)。细胞培养48和72 h时,与空白对照组和阴性对照组比较,Frat2-siRNA组和Frat2-siRNA+XAV组细胞增殖活性降低(P<0.05);与Frat2-siRNA组比较,Frat2-siRNA+XAV组细胞增殖活性降低(P<0.05);与空白对照组比较, 阴性对照组细胞增殖活性差异无统计学意义(P>0.05)。见表 3

表 3 各组NCI-H1688细胞增殖活性 Tab. 3 Proliferation activities of NCI-H1688 cells in various groups 
(n=7, x±s)
Group Proliferation activity
(t/h) 24 48 72
Blank control 0.39±0.07 0.79±0.13 1.35±0.24
Negative control 0.38±0.06 0.76±0.14 1.29±0.23
Frat2-siRNA 0.33±0.08 0.52±0.12*△ 0.81±0.18*△
Frat2-siRNA+XAV 0.30±0.06 0.36±0.09*△# 0.63±0.16*△#
F 2.724 19.849 20.938
P 0.067 <0.01 <0.01
*P<0.05 compared with blank control group;P<0.05 compared with negative control group;#P<0.05 compared with Frat2-siRNA group.
2.4 各组不同细胞周期NCI-H1688细胞百分率

与空白对照组和阴性对照组比较,Frat2-siRNA组和Frat2-siRNA+XAV组细胞中G0 /G1期细胞百分率明显升高(P<0.05),S期和G2/M期细胞细胞百分率明显降低(P<0.05);与Frat2-siRNA组比较,Frat2-siRNA+XAV组细胞中G0/G1期细胞百分率升高(P<0.05),S期和G2/M期细胞百分率降低(P<0.05);与空白对照组比较,阴性对照组不同周期细胞百分率差异无统计学意义(P>0.05)。见表 4图 3

表 4 各组不同细胞周期NCI-H1688细胞百分率 Tab. 4 Percentages of NCI-H1688 of cells in different cell cycles in various groups 
(n=7, x±s, η/%)
Group G0/G1 S G2/M
Blank control 57.46±3.25 24.06±1.35 18.48±1.02
Negative control 58.38±3.61 23.12±1.42 18.50±0.96
Frat2-siRNA 66.59±3.72*△ 19.83±1.52*△ 13.58±0.87*△
Frat2-siRNA+XAV 78.73±3.81*△# 16.27±1.39*△# 5.00±0.93*△#
F 52.350 43.275 316.290
P <0.01 <0.01 <0.01
*P<0.05 compared with blank control group;P<0.05 compared with negative control group;#P<0.05 compared with Frat2-siRNA group.
A: Blank control group; B: Negative control group; C:Frat2-siRNA group; D:Frat2-siRNA+XAV group. 图 3 流式细胞术检测各组不同细胞周期NCI-H1688细胞百分率 Fig. 3 Percentages of NCI-H1688 cells in different cell cycles in various groups detected by flow cytometry
2.5 各组NCI-H1688细胞中PCNA、c-myc和Cyclin D1蛋白表达水平

与空白对照组和阴性对照组比较,Frat2-siRNA组和Frat2-siRNA+XAV组细胞中PCNA、c-myc和Cyclin D1蛋白表达水平明显降低(P<0.05);与Frat2-siRNA组比较,Frat2-siRNA+XAV组细胞中PCNA、c-myc和Cyclin D1蛋白表达水平进一步降低(P<0.05);与空白对照组比较,阴性对照组细胞中PCNA、c-myc和Cyclin D1蛋白表达水平差异无统计学意义(P>0.05)。见表 5图 4

表 5 各组NCI-H1688细胞中PCNA、c-myc和Cyclin D1蛋白表达水平 Tab. 5 Expression levels of PCNA, c-myc and Cyclin D1 proteins in NCI-H1688 cells in various groups 
(n=7, x±s)
Group PCNA c-myc Cyclin D1
Blank control 0.53±0.11 0.95±0.16 0.38±0.07
Negative control 0.49±0.12 0.93±0.14 0.37±0.08
Frat2-siRNA 0.22±0.06*△ 0.52±0.15*△ 0.25±0.06*△
Frat2-siRNA+XAV 0.10±0.05*△# 0.21±0.11*△# 0.11±0.05*△#
F 37.362 44.313 25.680
P <0.01 <0.01 <0.01
*P<0.05 compared with blank control group;P<0.05 compared with negative control group;#P<0.05 compared with Frat2-siRNA group.
Lane 1:Blank control group; Lane 2:Negative control group; Lane 3:Frat2-siRNA group; Lane 4:Frat2-siRNA+XAV group. 图 4 Western blotting法检测各组NCI-H1688细胞中PCNA、c-myc和Cyclin D1蛋白表达电泳图 Fig. 4 Electrophoresgram of expressions of PCNA, c-myc, Cyclin D1 proteins in NCI-H1688 cells in various groups detected by Western blotting method
2.6 各组NCI-H1688细胞中β-catenin和pGSK-3β蛋白表达水平

与空白对照组和阴性对照组比较,Frat2-siRNA组和Frat2-siRNA+XAV组细胞中β-catenin和pGSK-3β蛋白表达水平明显降低(P<0.05);与Frat2-siRNA组比较,Frat2-siRNA+XAV组细胞中β-catenin和pGSK-3β蛋白表达水平明显降低(P<0.05);与空白对照组比较,阴性对照组细胞中β-catenin和pGSK-3β蛋白表达水平差异无统计学意义(P>0.05)。见表 6图 5

表 6 各组NCI-H1688细胞中β-catenin和pGSK-3β蛋白表达水平 Tab. 6 Expression levels of β-catenin and pGSK-3βproteins in NCI-H1688 cells in various groups 
(n=7, x±s)
Group β-catenin pGSK-3β
Blank control 0.67±0.13 0.86±0.15
Negative control 0.66±0.14 0.85±0.16
Frat2-siRNA 0.32±0.11*△ 0.35±0.10*△
Frat2-siRNA+XAV 0.15±0.09*△# 0.14±0.09*△#
F 32.823 55.577
P <0.01 <0.01
*P<0.05 compared with blank control group;P<0.05 compared with negative control group;#P<0.05 compared with Frat2-siRNA group.
Lane 1:Blank control group; Lane 2:Negative control group; Lane 3:Frat2-siRNA group; Lane 4:Frat2-siRNA+XAV group. 图 5 Western blotting法检测各组NCI-H1688细胞中β-catenin和pGSK-3β蛋白表达电泳图 Fig. 5 Electrophoregram of expressions of β-catenin and pGSK-3β proteins in NCI-H1688 cells in various groups detected by Western blotting method
3 讨论

小细胞肺癌虽占全部肺癌的比例较少,但其发展快,恶性程度高,在早期可发生远处转移,大部分患者确诊时已有血行或淋巴转移,自然病程比较短;小细胞肺癌虽对放化疗比较敏感,但大部分患者治疗后可出现复发和转移[6]。因此探讨小细胞肺癌的发生发展机制,对小细胞肺癌的诊断及治疗具有重要意义。Frat位于第10号染色体长臂上,其主要功能是与GSK3结合,抑制GSK3对β-catenin的磷酸化,在wnt信号转导通路中起正向调节作用。Frat包括Frat1和Frat2,Frat1由279个氨基酸构成,相对分子质量为29 000;Frat2由233个氨基酸构成,相对分子质量为24 000。Frat1和Frat2有77%的氨基酸构成相同,与GSK-3β结合区的氨基酸全部相同;Frat1和Frat2均为Wnt信号通路的正向调节因子[7]。目前关于Frat1在恶性肿瘤中作用的研究较多,如MiR-34a-3p靶向Frat1可改变脑膜瘤细胞的增殖和凋亡[8];Frat1过表达可调节结肠癌细胞的增殖[9];沉默Frat1可抑制SGC7901人胃腺癌细胞增殖[10];敲低Frat1可通过抑制肝细胞癌细胞中的Wnt /β-catenin信号通路抑制缺氧诱导的上皮-间质转化[11];沉默Frat1基因可通过下调β-catenin表达影响结肠癌HT-29细胞增殖和凋亡[12];Frat1参与了前列腺癌的发生发展过程[13]。关于Frat2的研究较少,STOOTHOFF等[14]研究发现:Frat2与GSK-3β结合导致底物发生磷酸化从而发挥生物学效应。但Frat2在肺癌中的作用尚不清楚。本研究结果显示:沉默Frat2后NCI-H1688细胞中Frat2表达水平降低,NCI-H1688细胞增殖活性降低,表明Frat2可能参与小细胞肺癌的发生发展过程。

PCNA是DNA复制过程中所必需的蛋白,相对分子质量为36 000,在细胞核中合成,在G0 /G1期细胞中表达不明显,在G1晚期细胞中表达水平增加,S期细胞中表达水平达高峰,G2 /M期细胞中表达水平明显降低,与DNA的变化一致,是细胞增殖状态的标志物之一[15-16]。c-myc为myc家族成员,既是一种可易位基因,也是一种可调节基因,可使细胞获得永生化功能,使细胞无限增殖,促进细胞分裂,可决定细胞周期能否从G0 /G1期向S期过渡,是一种细胞恶性的标志物之一,与恶性肿瘤细胞的恶性增殖关系密切[17-18]。Cyclin D1为G1/S期特异性周期蛋白D1,属于高度保守的细胞周期家族成员之一,主要功能为促进细胞增殖,其作用在于作为细胞周期蛋白依赖性激酶的调控者,结合并激活G1期细胞特有的周期蛋白依赖性激酶CDK4,磷酸化G1期周期抑制蛋白,使其从所结合的E2F上解离,推动细胞周期从G1期进入S期[19-20]。本研究结果显示:沉默Frat2后NCI-H1688细胞中PCNA、c-myc和Cyclin D1蛋白表达水平降低,表明沉默Frat2可通过阻止G1期细胞向S期过渡进而抑制NCI-H1688细胞的增殖。

Wnt信号通路在恶性肿瘤细胞增殖中发挥重要作用,在肺癌的发生发展中也发挥重要作用。β-catenin为Wnt信号通路的关键调控因子,Wnt信号通路在正常成熟细胞中处于关闭状态,在病理状态下,Wnt信号通路被激活,β-catenin去磷酸化,进入细胞核与T细胞因子(T cell factor, TCF)/淋巴增强因子(lymphoid enhancer factor, LEF)结合开启下游的PCNA、c-myc和Cyclin D1等靶基因的转录,从而抑制恶性肿瘤细胞的增殖[21-22]。pGSK-3β是Wnt通路的关键调节因子,通过影响β-catenin参与调控细胞增殖和凋亡;经典Wnt通路激活后抑制由GSK-3β和轴蛋白等组成的复合体中的GSK-3β磷酸化,避免β-catenin被泛素蛋白酶体识别及降解,并与TCF/LEF结合导致细胞增殖异常,从而促进恶性肿瘤发生发展[23-24]。Wnt/β-catenin信号通路在肺癌细胞的增殖中发挥重要作用,且位于Frat2和Frat1与GSK-3β结合区的氨基酸全部相同,Frat2也可与GSK-3β结合发挥作用,进而调节Wnt信号通路,因此推测Frat2可能通过Wnt/β-catenin信号通路影响小细胞肺癌细胞的增殖。本研究结果显示:沉默Frat2后NCI-H1688细胞中β-catenin和pGSK-3β蛋白表达水平降低;对NCI-H1688细胞给予Wnt信号通路抑制剂XAV939后,NCI-H1688细胞的增殖能力降低,细胞被阻止在G0/G1期,细胞中PCNA、c-myc、Cyclin D1、β-catenin和pGSK-3β蛋白水平降低,表明沉默Frat2及给予Wnt信号通路抑制剂处理均可抑制小细胞肺癌细胞增殖、阻止细胞周期进程、抑制Wnt/β-catenin信号通路激活。由此可见Frat2可能通过Wnt/β-catenin信号通路抑制NCI-H1688细胞增殖。

综上所述,Frat2在小细胞肺癌NCI-H1688细胞中高表达,沉默Frat2可通过Wnt/β-catenin信号通路抑制NCI-H1688细胞增殖。Frat2有望成为小细胞肺癌治疗的潜在靶点。

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