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在全球女性恶性肿瘤中,宫颈癌的发病率和病死率均居第4位[1]。2020年,全球有60.4万宫颈癌新发病例和34.2万宫颈癌死亡病例;中国约有11.0万例宫颈癌患者,其中包括5.9万死亡病例[2]。目前,宫颈癌的治疗方法包括手术、化疗和放疗等[3]。宫颈癌Ⅰ B3~ⅣB期患者均需行放疗,然而约30%接受放疗的患者会出现肿瘤复发[4]。因此,研究影响宫颈癌细胞在放疗后DNA损伤修复的分子机制对提高宫颈癌的放疗效果具有重要意义。
表皮生长因子受体(epidermal growth factor receptor,EGFR)是由原癌基因c-erbB1编码的Ⅰ型跨膜酪氨酸激酶受体(TKR),其由1 210 个氨基酸构成,相对分子质量约为170 000。EGFR分为3个部分:与配体结合的细胞外结构域、跨膜结构域和含有酪氨酸激酶活性的细胞内结构域。EGFR被认为与多种癌症的预后有关,如头颈癌、肺癌、食道癌和胃癌[5]。有研究报道,EGFR信号通路在细胞的生长、增殖和分化等生理过程中发挥重要作用,其过表达或扩增在宫颈癌中发挥调控细胞辐射抗性的作用[6]。
核转录因子E2相关因子2(nuclear factor-E2-related factor 2,NRF2)在保护细胞免受氧化、亲电等多种环境因素威胁,维持暴露在辐射或药物下的细胞内的氧化还原动态平衡方面具有重要作用。有研究结果证明,肿瘤细胞中NRF2的过表达通常与辐射和化学耐药性有关[7]。有文献报道,在黑色素瘤细胞中,NRF2可以促进EGFR的激活,而在口腔癌细胞中EGFR可以促进NRF2的激活[8-9]。但在宫颈癌细胞中,关于EGFR和NRF2在辐射诱导的DNA损伤修复中的关系目前鲜见报道。本研究旨在探讨辐射后的宫颈癌HeLa细胞中EGFR和NRF2对DNA损伤修复的影响及其二者之间的相互关系,为指导宫颈癌的放疗提供理论依据。
EGFR和NRF2对电离辐射导致的DNA损伤修复的影响
The effects of EGFR and NRF2 on DNA damage repair induced by ionizing radiation
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摘要:
目的 探讨表皮生长因子受体(EGFR)和核转录因子E2相关因子2(NRF2)对人宫颈癌HeLa细胞受到电离辐射损伤后的DNA损伤响应及修复作用。 方法 将人宫颈癌HeLa细胞按2种处理方式分组:(1)采用小干扰RNA敲降HeLa细胞中的EGFR,采用137Cs γ射线照射源照射细胞。将HeLa细胞分为对照组(HeLa siCtrl)、敲降EGFR组(HeLa siEGFR)、照射组(HeLa siCtrl+8 Gy)、敲降EGFR+照射组(HeLa siEGFR+8 Gy)。采用免疫荧光实验(8 Gy照射后6、12、24 h)检测细胞中磷酸化组蛋白H2A变异体(γ-H2AX)foci的数量;采用实时荧光定量聚合酶链式反应(RT-qPCR)检测NRF2下游靶基因;采用流式细胞术检测EGFR对HeLa细胞周期的影响;采用核质分离实验分离HeLa细胞的胞质蛋白和胞核蛋白;采用蛋白质免疫印迹法检测NRF2、EGFR、血红素氧合酶1(HO-1)、共济失调毛细血管扩张突变基因Rad3相关激酶(ATR)Thr1989位点的磷酸化水平、检查点激酶1(CHK1)在Ser345位点的磷酸化水平。(2)采用小干扰RNA敲降HeLa细胞中的NRF2,采用137Cs γ射线照射源照射细胞。将HeLa 细胞分为对照组(HeLa siCtrl)、敲降NRF2组(HeLa siNRF2)、照射组(HeLa siCtrl+8 Gy)、敲降NRF2+照射组(HeLa siNRF2+8 Gy)。采用免疫荧光实验检测细胞中γ-H2AX foci的数量。符合正态分布的计量资料的组间比较采用两独立样本t检验(方差齐)。 结果 (1)8 Gy照射6、12、24 h后,HeLa siEGFR+8 Gy组细胞中γ-H2AX foci的数量均多于HeLa siCtrl组[(94.00±1.00)% 对(89.67±2.03)%、(72.33±1.76)% 对(60.00±1.73)%、(43.00±2.31)% 对(26.33±1.20)%],且差异有统计学意义(t=3.919、4.919、6.402,均P<0.05)。与HeLa siCtrl组比较,HeLa siEGFR+8 Gy组的细胞G2/M期阻滞显著受损[(46.53±3.06)%对(37.90±4.61)%],且差异有统计学意义(t=4.384,P<0.05)。与HeLa siCtrl组比较,HeLa siEGFR+8 Gy组的HO-1表达下降66.66%(1.35±0.10对0.45±0.02),且差异有统计学意义(t=8.782,P<0.05)。敲降EGFR后细胞核内的NRF2蛋白水平降低,辐射引起的NRF2下游ATR-CHK1信号通路活化水平及HO-1蛋白水平均降低。(2)8 Gy照射6、12、24 h后,与HeLa siCtrl组相比,HeLa siNRF2+8 Gy组细胞中γ-H2AX foci的数量均多于HeLa siCtrl组[(96.67±0.88)%对(89.67±2.03)%、(77.33±1.20)% 对(60.00±1.73)%、(54.33±2.19)% 对(26.33±1.20)%],且差异均有统计学意义(t=3.166、4.919、11.220,均P<0.05)。 结论 电离辐射条件下,敲降EGFR可以减少NRF2蛋白入核,抑制ATR-CHK1信号通路激活及下游基因HO-1的表达,降低人宫颈癌HeLa细胞的DNA损伤修复能力。 -
关键词:
- 宫颈肿瘤 /
- DNA损伤 /
- DNA修复 /
- 表皮生长因子受体 /
- 核转录因子E2相关因子2
Abstract:Objective To investigate the effect of epidermal growth factor receptor (EGFR) and nuclear factor-E2-related factor 2(NRF2) on DNA damage response and repair in human cervical cancer HeLa cells after exposure to ionizing radiation. Methods Human cervical cancer HeLa cells were treated in two groups. (1) EGFR was knocked down in HeLa cells using a small interfering RNA, and the cells were irradiated using a 137Cs γ-ray irradiation source. HeLa cells were divided into control group (HeLa siCtrl), knockdown EGFR group (HeLa siEGFR), irradiation group (HeLa siCtrl+8 Gy), and knockdown EGFR+irradiation group (HeLa siEGFR+8 Gy). The number of phosphorylated histone 2A variant (γ-H2AX) foci in the cells was detected by immunofluorescence assay (6, 12, and 24 h after 8 Gy irradiation); the NRF2 downstream target genes were detected by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) assay; the expression levels of flow cytometry were used to detect the effect of EGFR on HeLa cell cycle; nucleoplasmic separation assay was used to isolate cytoplasmic and cytosolic proteins from HeLa cells; protein immunoblotting was used to detect the phosphorylation levels of NRF2, EGFR, HO-1, ataxia-telangiectasia mutated gene and Rad3-related kinase (ATR) Thr1989 locus, cell cycle checkpoint kinase 1 (p-CHK1), and Ser345 site phosphorylation level. (2) A small interfering RNA was used to knock down NRF2 in HeLa cells, and the cells were irradiated with a 137Cs γ-ray irradiation source. HeLa cells were divided into control group (HeLa siCtrl), knockdown NRF2 group (HeLa siNRF2), irradiation group (HeLa siCtrl+8 Gy), and knockdown NRF2+ irradiation group (HeLa siNRF2+8 Gy). An immunofluorescence assay was used to detect the number of γH2AX foci in HeLa cells. Inter-group comparisons of measures conforming to normal distribution were performed by two independent sample t-tests (chi-squared). Results (1) After 8 Gy irradiation for 6, 12, and 24 h, the number of γH2AX foci in HeLa siEGFR+8 Gy were more than that HeLa siCtrl ((94.00±1.00)% vs. (89.67±2.03)%, (72.33±1.76)% vs. (60.00±1.73)%, (43.00±2.31)% vs. (26.33±1.20)%), and the differences were statistically significant (t=3.919, 4.989, 6.402; all P<0.05). The HeLa siEGFR+8 Gy impaired radiation-induced G2/M phase cell cycle block compared with the HeLa siCtrl, ((46.53±3.06)% vs. (37.90±4.61)%), and the difference was statistically significant (t=4.384, P<0.05). Compared with the HeLa siCtrl, HeLa siEGFR+8 Gy inhibited the radiation induced decrease in HO-1 expression by 66.66%(1.35±0.10 vs. 0.45±0.02), and the difference was statistically significant (t=8.782, P<0.05). The level of NRF2 protein in the nucleus was reduced after knocking down EGFR, and the radiation-induced activation level of the ATR-CHK1 signaling pathway downstream of NRF2 and the level of HO-1 protein were reduced. (2) After 8 Gy irradiation for 6, 12, and 24 h, the number of γH2AX foci in HeLa siNRF2+8 Gy was more than that HeLa siCtrl ((96.67±0.88)% vs. (89.67±2.03)%, (77.33±1.20)% vs. (60.00±1.73)%, (54.33±2.19)% vs. (26.33±1.20)%), and all differences were statistically significant (t=3.166, 4.989, 11.220; all P<0.05). Conclusions Under ionizing radiation conditions, knocking down EGFR can reduce the nuclear translocation of NRF2 protein, inhibit the activation of the ATR-CHK1 signaling pathway and the downstream expression of the HO-1 gene, and decrease the DNA damage repair capacity of human cervical cancer HeLa cells. -
图 4 照射和未照射条件下敲降EGFR后HeLa细胞中EGFR、NRF2蛋白在细胞质和细胞核中表达水平的比较
Figure 4. Comparison of epidermal growth factor receptor and nuclear factor-E2-related factor 2 protein expression levels in cytoplasm and nucleus of HeLa cells after knocking down epidermal growth factor receptor under irradiation and non-irradiation conditions
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