siRNA沉默环指蛋白8基因对裸鼠人鼻咽癌移植瘤放疗增敏作用的实验研究

Silencing RNF8 by siRNA enhances the radiation sensitivity of NPC transplantation tumor in nude mice

目的探讨环指蛋白8(RNF8)的放疗抵抗作用及沉默RNF8后对鼻咽癌的放疗增敏作用及其机制。方法分别将鼻咽癌CNE-1细胞株及稳定转染的RNF8沉默的CNE-1细胞株注射入裸鼠背部皮下,建立裸鼠鼻咽癌移植瘤模型。将肿瘤长至直径8~10 mm的裸鼠30只按随机数字法分为RNF8未沉默组(RNF8+组)和RNF8沉默组(RNF8-组),每组按放疗照射剂量的不同又分5个亚组,每个亚组3只,分别给予0、4、8、12、16Gy照射,其中0 Gy为对照亚组。采用局部分割照射,每次2 Gy。照射完成10 d后杀鼠取瘤,称重观察抑瘤情况,计算抑瘤率;取2组8Gy剂量亚组肿瘤制成细胞悬液,应用流式细胞仪检测凋亡率,应用流式细胞仪检测2组8 Gy剂量亚组中RNF8和DNA依赖蛋白激酶催化亚单位(DNA-PKcs)、共济失调毛细血管扩张症突变基因(ATM)的表达。结果RNF8在RNF8-组中只有微量表达(0.11±0.03),而在RNF8+组中表达明显升高(1.18±0.23),差异有统计学意义(P<0.01)。RNF8+组和RNF8-组分别在16 Gy时抑瘤率最大。RNF8+组抑瘤率在各个剂量点均低于RNF8-组,其中8 Gy时差异最大(P<0.01)。因此选择RNF8+组8 Gy剂量亚组和RNF8-组8 Gy剂量亚组进行比较。RNF8+组8 Gy剂量亚组凋亡率明显低于RNF8-组8 Gy剂量亚组(P<0.05)。RNF8+组8 Gy剂量亚组中ATM表达(49.3±5.3)较RNF8-组8 Gy剂量亚组(23.4±2.6)明显升高(P<0.01),而DNA-PKcs在组间表达差异无统计学意义(P>0.05)。结论RNF8可以导致鼻咽癌细胞的放疗抵抗,其机制是通过激活以ATM为主的同源重组(HR)途径来修复损伤的肿瘤细胞DNA,沉默RNF8可以增加鼻咽癌的放疗敏感性。

Objective To explore the role of RNF8 in radioresistance ofnasopharyngeal cancer(NPC)and the irradiation enhancement effect and mechanism to NPC when RNF8 was silenced.Methods CNE-1 cells and CNE-1 cells in which RNF8 was stably silenced by siRNA were injected to the back of nude mice subcutaneously,respectively.The model of NPC transplantation tumor in nude mice was established.Thirty nude mice with 8-10 mm transplanted tumor were divided to two groups:RNF8+Group(RNF8 not silenced)and RNF8-Group(RNF8 silenced).Each group was divided to 4 sub-groups and 1 control group.Each sub-group had 3 mice.Tumor of mice in sub-groups received 4 Gy,8 Gy,12 Gy and 16 Gy irradiation,respectively.Mice in control groups were received 0 Gy.Local fractional irradiation was used for mice with 2 Gy each time.Mice were killed 10 days after irradiation,then tumors were taken out and weighed.Tumor inhibition rate was calculated.Tumors in 8 Gy sub-group of RNF8+Group and 8 Gy sub-group of RNF8-Group were made to cell suspension.The apoptosis rate were detected by flow cytometry.The expression of RNF8,DNA-PKcs and ATM was detected in the cell suspension by flow cytometry.Results RNF8 was higher expressed in RNF8+Group(1.18±0.23)than that in RNF8-Group(0.11±0.03,P<0.01).Tumor inhibition rate was the highest when they received 16 Gy radiation in both groups.Tumor inhibition rate in RNF8-Group at every dose point was higher than that in RNF8+Group,the largest gap was at 8 Gy dose point(P<0.01).The detection index of 8 Gy sub-group of RNF8+Group was compared to that of 8 Gy sub-group of RNF8-Group.The apoptosis rate in 8 Gy sub-group of RNF8-Group was higher than that in 8 Gy sub-group of RNF8+Group(P<0.05).The expression of ATM in 8 Gy sub-group of RNF8+Group(49.3±5.3)was significantly higher than that in 8 Gy sub-group of RNF8-Group[(23.4±2.6),P<0.01].The expression of DNA-PKcs had no significant differences between both groups(P>0.05).Conclusion RNF8,which can activate homologous recombination(HR)way to repair impaired DNA of cancer cells,mediates the radioresistance of NPC cells.Silencing RNF8 can enhance radiation sensitivity of NPC.