The role of DNA damage repair and Chk2 protein in hyper-radiosensitivity of lung adenocarcinoma A549 cells

To explore the role of the Chk2 protein expression and DNA double strand breaks (DSBs) repair in low dose hyper-radiosensitivity (HRS)/increased radioresistance (IRR) of non-small cell lung cancer,A549 cells were subjected to irradiation at the dosage ranging from 0.05-2 Gy.Clonogenic survival was measured by using fluorescence-activated cell sorting (FACS) plating technique.Percentage of cells in M-phase after low doses of X-irradiation was evaluated by phospho-histone H3-FITC/PI and Western blotting was used to detect protein expression of Chk2 and phospo-Chk2.DNA DSBs repair efficiency was also measured by induction and persistence of γ-H2AX.The results showed that the killing ability of irradiation with A549 cells increased at low conditioning dose below 0.3 Gy.Within the dose of 0.3 to 0.5 Gy,A549 cells showed a certain extent of radiation resistance.And when the dose was more than 0.5 Gy,survival fraction exhibited a negative correlation with the dosage.There was no difference between the 0.1 or 0.2 Gy dosage groups and the un-irradiated group in terms of the percentage of cells in M phase.But in the high dosage group (0.3-1.0 Gy),the percentage of cells in M phase was decreased markedly.In addition,the percentage of cells in M phase began to decrease two hours after irradiation.One hour after irradiation,there was no conspicuous activation of Chk2 kinase in 0.1 or 0.2 Gy group,but when the irradiation dose reached 0.3 Gy or higher,Chk2 kinase started to be activated and the activation level showed no significant difference among high dosage groups (0.4,0.5,1.0 Gy).Within 1 to 6 h,the DNA DSBs repair efficiency was decreased at 0.2 Gy but increased at 0.5 Gy and 1.0 Gy,which was in line with Chk2 activation.We are led to conclude that the mechanism of HRS/IRR in A549 cell line was probably due to early G2/M checkpoint arrest and enhanced DNA DSBs repair.In this regard,Chk2 activation plays a key role in G2/M checkpoint activation.     

早期 G2期检查点与细胞低剂量放射超敏感性或增强的放射抗性现象相关性研究进展

低剂量放射超敏感性或增强的放射抗性(low-dose hyperradiosensitivity/increased radioresistance,HRS/IRR)现象自发现以来,以其巨大潜在临床应用价值,一直是国际上研究热点。国内外主要从细胞凋亡、细胞周期检查点调控、DAN损伤识别和修复等几个方面进行了大量研究来阐明HRS/IRR现象的分子机制。目前研究支持低剂量放射下早期 G₂期检查点阻滞缺失导致DNA双链断裂(double strand breaks,DSB)修复效率降低是细胞发生HRS/IRR现象的主要机制。笔者着重讨论人毛细血管扩张性共济失调突变基因(ataxia-telangiectasia mutation,ATM)依赖性的早期 G₂期检查点在细胞HRS/IRR现象中的作用。     

乳腺癌的分子靶向治疗新进展

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