Institute of Radiation Medicine, Fudan University, No.2094 Xie-Tu Road, Shanghai 200032, China.
Br J Cancer. 2012 Feb 28;106(5):889-95. doi: 10.1038/bjc.2012.9. Epub 2012 Jan 24.
Radiation-induced bystander effect (RIBE) has important implication in tumour radiotherapy, but the bystander signals are still not well known.
The role of cytochrome-c (cyt-c) and free radicals in RIBE on human hepatoma cells HepG2 was investigated by detecting the formation of bystander micronuclei (MN) and the generation of endogenous cyt-c, inducible nitric oxide (NO) synthase (iNOS), NO, and reactive oxygen species (ROS) molecules.
When HepG2 cells were cocultured with an equal number of irradiated HepG2 cells, the yield of MN in the nonirradiated bystander cells was increased in a manner depended on radiation dose and cell coculture time, but it was diminished when the cells were treated with cyclosporin A (CsA), an inhibitor of cyt-c release. Meanwhile the CsA treatment inhibited radiation-induced NO but not ROS. Both of the depressed bystander effect and NO generation in the CsA-treated cells were reversed when 5 μM cyt-c was added in the cell coculture medium. But these exogenous cyt-c-mediated overproductions of NO and bystander MN were abolished when the cells were pretreated with s-methylisothiourea sulphate, an iNOS inhibitor.
Radiation-induced cyt-c has a profound role in regulating bystander response through an iNOS-triggered NO signal but not ROS in HepG2 cells.
辐射诱导的旁观者效应（RIBE）在肿瘤放射治疗中有重要意义，但旁观者信号仍不清楚。
通过检测人肝癌细胞 HepG2 中旁观者微核（MN）的形成和细胞色素 c（cyt-c）、诱导型一氧化氮合酶（iNOS）、NO 和活性氧（ROS）分子的内源性产生，研究 cyt-c 和自由基在 RIBE 中的作用。
当 HepG2 细胞与同等数量的辐照 HepG2 细胞共培养时，未辐照旁观者细胞中 MN 的产量以依赖于辐射剂量和细胞共培养时间的方式增加，但当用细胞色素 c 释放抑制剂环孢菌素 A（CsA）处理时，MN 的产量减少。同时，CsA 处理抑制了辐射诱导的 NO，但不抑制 ROS。在用细胞共培养培养基中添加 5 μM cyt-c 处理时，CsA 处理的细胞中旁观者效应和 NO 生成的抑制作用得到逆转。但当用 iNOS 抑制剂 S-甲基异硫脲硫酸盐预处理细胞时，这些外源性 cyt-c 介导的 NO 和旁观者 MN 的过度产生被消除。
辐射诱导的 cyt-c 通过 iNOS 触发的 NO 信号而不是 HepG2 细胞中的 ROS，在调节旁观者反应中起重要作用。
