中文摘要：

近年来临床研究发现,艾滋病合并肿瘤患者放疗后产生的正常组织和皮肤毒性反应明显高于普通肿瘤患者.本研究将探讨HIV-1Tat蛋白是否影响细胞对电离辐射敏感性及机理.两个表达Tat蛋白的细胞系TT2和TE671-Tat均来源于人的横纹肌肉瘤细胞（TE671）并已转染了不同来源的tat基因.使用细胞辐射后克隆形成率检测辐射敏感性,RT-PCR和Western印迹检测基因表达,彗星电泳和γ-H2AX位点检测DNA双链断裂和修复.TT2和TE671-Tat细胞的辐射敏感性与转染空载体及对照细胞相比明显增加.彗星电泳和γ-H2AX位点检测表明,在表达Tat蛋白的细胞中,辐射诱导DNA双链断裂的修复水平明显降低.通过RT-PCR和Western印迹检测进一步证实,表达Tat蛋白的细胞中DNA修复蛋白DNA-PKcs的表达被抑制.HIV-1Tat蛋白抑制DNA-PKcs的表达,降低DNA双链断裂的修复,使细胞的电离辐射敏感性增高.本研究为了解AIDS合并肿瘤患者对放射治疗敏感性变化提供了重要信息.

英文摘要：

There is accumulating evidence that HIV-1/AIDS cancer patients have more severe tissue reactions and often develop cutaneous toxic effects when subjected to radiotherapy. Here we explored the effects of the HIV-1 Tat protein on cellular responses to ionizing radiation and related mechanism. Two Tat-expressing cell lines TT2 and TE671-Tat were derived from human rhabdomyosarcoma cells by transfecting with the HIV-1 tat gene. Radiosensitivity was determined using colony-forming ability. Gene expression was assessed by RT-PCR and immuno-hybridization. The Comet assay and γ-H2AX foci were employed to detect DNA double-strand breaks （DSBs） and repair. The radiosensitivity of TT2 and TE671-Tat cells was significantly increased as compared with parental TE671 cells or the control TE671-pCI cells. The comet assay and γ-H2AX foci detection revealed a decreased capacity to repair radiation-induced DNA DSBs in Tat-expressing cells. Depression of DNA-PKcs in Tat-expressing cells was further confirmed by RT-PCR and immuno-hybridization analysis. HIV-1 Tat protein sensitizes cells to ionizing radiation via, at least partially, depressing DNA-PKcs expression and DNA repair. These observations provide new information into the increased tissue reactions of AIDS cancer patients to radiotherapy.