hMRE11在依托泊甙所致U937细胞DNA双链断裂后的修复中发挥重要作用(英文)

hMRE11 Plays an Important Role in U937 Cellular Response to DNA Double-Strand Breaks Following Etoposide

MRE11在DNA损伤反应的信号转导通路中起着重要的作用。本研究查明hMRE11与依托泊甙所致人单核细胞白血病细胞株U937DNA双链断裂的关系。在依托泊甙(VP-16)处理U937细胞后,运用脉冲凝胶电泳(PFGE)检测DNA双链断裂,采用RT-PCR技术检测MRE11的转录水平,借助免疫荧光技术检测hMRE11蛋白的分布改变,并通过流式细胞术检测其细胞周期。结果表明:VP-16诱导U937细胞DNA双链断裂的发生率与其剂量高度相关,从2μg/ml时的(13.0±2.3)%增至20μg/ml时的(32.0±4.3)%(P<0.01)。但VP-16诱导U937细胞前后不同时间内hMRE11mRNA水平未见变化(P>0.05)。hMRE11蛋白丰富而均匀分布于核仁外的细胞核中,但经VP-16处理后则形成独立的核灶(nuclearfocus),并且存在这种核灶的细胞数和细胞中的核灶数量随VP-16的剂量增加而增多。经100μg/mlVP-16处理(2小时)后8小时形成hMRE11蛋白灶的U937细胞数达到(61.54±3.6)%[对照组为(0.47±1.17)%,P<0.01],而且47.55±2.35%的U937细胞[对照组(21.95±2.91)%,P<0.05]停滞于S期,然后逐渐下降。结论:hMRE11蛋白核灶形成可能参与VP-16所致人单核白血病细胞株U937的DNA损伤修复过程。

MRE11 plays an important role in the signal transduction of DNA damage response, therefore this study was purposed to explore the relationship between hMRE11 focus formation and DNA double-strand breaks （DSBs） caused by etoposide（VP-16） in human promonocytic cells U937 After U937 cells were treated with VP-16, the drug-induced DSBs were assessed by pulsed-field gel electrophoresis （PFGE）, the gene transcription levels of hMRE11 were evaluated by RT-PCR, the nuclear focus formation of hMRE11 protein was examined using immunofluorescence technique, the cell cycle in parallel was analyzed by flow cytometry. The results showed that the percentage of U937 cells with DSBs induced byVP-16 raised from 13. 0 ± 2. 3% in VP-16 2 μg/l to 32. 0 ±4. 3% in VP-16 20 ±g/ml（P 〈 0.01 ） along with increase of VP-16 dose. No difference of the hMREll mRNA level in U937 ceils following the treatment with 100 μg/l VP-16 at different times was discovered（ P 〉 0.05 ）. The hMRE11 protein was abundantly and uniformly distributed in the nuclei of untreated U937 cells outside of nucleoli, however, it formed discrete nuclear foci following VP-16 treatment. The mean value of nuclear foci increased by 5 to 20 times following the drug dosing （ P 〈 0.01 ）. An average of 5 nuclear foci per positive nucleus were observed at a dose of 2 μg/l, and it was increased to an average of over 14 nuclear foci per positive nucleus after treating with VP-16 20 μg/l, The percentage of nuclei containing hMRE11 nuclear foci also increased from less than 10% after treatment wiht VP-16 2 μg/ml to over 50% after VP-16 20 μg/ml（P 〈0.01 ） following treatment with VP-16. After U937 cells were treated with 100 μg/ml VP-16 for 2 hours and fixed at 4, 8, 12 and 24 hours, the percentage of nuclei with hMRE11 nuclear foci increased to 61.54 ± 3.6% （the control U937 ceils ：0.47 ± 1.17% , P 〈 0.01 ）at 8 hours, with a subsequent decrease in the percentage of nuclear foci -positive cells by 24 hours. The ratio of S-phase U937 cells at 8 hours after being treated with 100 μg/ml VP-16 for 2 hours was 47.55 ± 2.35 %, and that without 100 μg/ml VP-16 was 21.95 ± 2.91% （ P 〈 0.05 ）. It is concluded that the nuclear focus formation of hMREll protein may be a response to DNA damage induced by topoisomerase Ⅱ inhibitor VP-16 in human promonocytic cell line U937.