乏氧条件下SirT1参与的肝癌辐射旁效应对増敏和毒副作用的双重影响及机制

Radiation-induced bystander effect not only enhances tumor sensitivity, but also has toxic effect on normal cells, which are the coexistence and paradoxical factors during cancer radiotherapy, and play a crucial role in restricting the improvement of the efficiency of clinic cancer radiotherapy. Our previous research demonstrated that silent information regulator 1 (SirT1) participated in radiation-induced bystander effect which caused DNA damage for non-irradiated hepatoma cells as well as normal liver cells, and the effect of SirT1 on radiation-induced bystander effect was influenced by tumor hypoxic microenvironment. Based on our previous study and the latest associated research progress, we intend to carry out the following research proposal. 1. Examining the role of SirT1 on radiation-induced bystander effect under hypoxia, and analysing the different impact of SirT1 involved radiation-induced bystander on sensitizing hepatoma cells and toxic effect to normal liver cells under normoxic and hypoxic conditions. 2. Investigating the molecular mechanism of SirT1 on radiation-induced bystander effect in irradiated hepatoma cells under different oxygen conditions. 3. Exploring the active modes of the signal factors regulated by SirT1 involved radiation-induced bystander effect on non-irradiated hepatoma cells and normal liver cells, and investigating the differences of their mechanisms. The results of this research will reveal the paradoxical regulation mechanism of SirT1 involved radiation-induced bystander effect on sensitizing hepatoma cells and toxic effect to normal liver cells, and will provide preliminary research foundation for molecular targeting guided cancer radiotherapy.

辐射旁效应既能增强肿瘤细胞的敏感性，又对正常细胞具有毒副作用，这正是肿瘤放疗中并存的矛盾因素，是制约肿瘤放疗疗效提高的关键瓶颈。我们新近的研究发现，沉默信息调节因子1（SirT1）参与的辐射旁效应在促进肝癌细胞DNA损伤的同时，也对正常细胞产生毒副作用，而且，SirT1参与的辐射旁效应受肿瘤乏氧微环境的影响。本课题拟在前期研究的基础上，首先观察乏氧条件下SirT1对受辐射肝癌细胞诱导旁效应的影响，并分析SirT1参与的辐射旁效应对肝癌细胞増敏和正常肝细胞毒副作用的差异；其次研究不同氧条件下SirT1调控受辐射肝癌细胞诱导旁效应的分子机制；最后探讨SirT1参与的辐射旁效应释放的信号因子对未受辐射的肝癌细胞和正常肝细胞作用靶点的差异及内在机制。本课题的实施有望揭示SirT1参与的辐射旁效应对肿瘤细胞增敏及对正常细胞毒副作用双重影响的机制，为肿瘤放射治疗中寻找新的靶点提供前期的研究基础。

辐射旁效应既能增强肿瘤细胞的放疗敏感性，又对正常细胞具有毒副作用，这对肿瘤放射治疗的疗效具有重要而复杂的作用。我们前期的研究表明，沉默信息调节因子1（SirT1）参与的辐射旁效应在促进肝癌细胞DNA损伤的同时，也对正常细胞产生毒副作用，而且，SirT1参与的辐射旁效应受肿瘤乏氧微环境的影响。为了探究其中的机制，我们开展了本课题。研究结果发现：有氧或乏氧条件下受辐射肝癌细胞的条件培养液均能明显增强未受辐射正常肝细胞的微核形成率，而且，乏氧条件下，受辐射肝癌细胞诱导正常肝细胞旁效应的损伤份额明显高于有氧条件下。乏氧条件下，SirT1基因对受辐射肝癌细胞诱导旁效应过程起着重要的抑制作用。SirT1基因干扰在受辐射肝癌细胞中可通过增强c-Myc蛋白的表达和转录活性，促进胞内ROS的累积并释放到外周，进而对正常肝细胞发挥辐射旁效应损伤作用。进一步的研究显示：受辐射肝癌细胞的条件培养液处理正常肝细胞时，可促发肝细胞产生内质网应激反应。适度的内质网应激反应通过激活PERK–p-eIF2α–CHOP信号通路，抑制肝细胞的DNA损伤和凋亡，从而抵御受辐射肝癌细胞诱导的旁效应损伤。以上研究成果，有利于推进对SirT1参与的辐射旁效应对肝癌细胞增敏及对正常肝细胞毒副作用双重影响的认识，为肝癌在放射治疗中寻找新的靶点提供有前景的策略和手段。