MUTATION INDUCTION BY CYTOPLASMIC IRRADIATION IN MAMMALIAN CELLS

细胞质辐射的生物学效应 哺乳动物细胞在很大程度上是未知的。使用微束在 放射研究加速器设施，我们检查了细胞 致死性、突变诱导和反应性的功能作用 人-仓鼠杂交(AL)细胞中的氧物种 通过其细胞的阿尔法粒子的准确数量(150keV/(M)) 细胞质。用双荧光染料和图像分析系统， 用来确定每个长端以外的照射位置 手机。与核辐射相比(Hei等人，PNAS。94： 3765,1997)，细胞质辐射引起的毒性最小 带有4个阿尔法粒子的细胞的遍历导致了一个存活的 约0.9的分数。当细胞质穿越1或2时 粒子在AL细胞中诱导的S1突变很少，经4 或更多的颗粒具有2.5倍的诱变比例 高于本底发病率。粒子传输和 成像系统的设计使得击中目标的机会 4粒子穿越，原子核只有0.4%。与之相对的是 主要由核穿越引起的多位点缺失， 细胞质辐射诱导的S1-突变体多为小突变体 类似于自发起源的改变。并发 8%DMSO处理细胞后致突变性显著降低 细胞质辐射的潜力。与之相反，前处理 细胞内含10 mM丁硫氨酸S-R亚磺胺，可降低细胞的 细胞非蛋白质巯基水平降至对照的5%以下 水平，显著提高了细胞质诱变的发生率 辐射。我们的结果首次表明，细胞质 (-粒子对哺乳动物细胞的穿透是通过 机制不同于核穿越，可能涉及 氧自由基。

The biological consequences of cytoplasmic irradiation in mammalian cells are largely unknown. Using the microbeam at the Radiological Research Accelerator Facility, we examined cell lethality, mutation induction and the functional role of reactive oxygen species in human-hamster hybrid (AL) cells traversed by an exact number of alpha particles (150 keV/(m) through their cellular cytoplasm. Dual fluorochrome dyes and an image analysis system were used to determine the irradiation positions off the long ends of each cell. In comparison to nuclear irradiation (Hei et al., PNAS. 94: 3765,1997), cytoplasmic irradiation induced minimal toxicity such that traversal of cells with 4 alpha particles resulted in a surviving fraction of ~0.9. While cytoplasmic traversal with either 1 or 2 particles induced few S1- mutants in AL cells, those irradiated with 4 or more particles had an induced mutant fraction that was 2.5 fold higher than the background incidence. The particle delivery and imaging systems are so designed such that the chance of hitting the nucleus is only 0.4% with 4 (-particle traversals. In contrast to the multilocus deletions predominately induced by nuclear traversals, S1-mutants induced by cytoplasmic irradiation involved mostly small alterations similar to those of spontaneous origin. Concurrent treatment of cells with 8% DMSO significantly reduced the mutagenic potential of cytoplasmic irradiation. In contrast, pretreatment of cells with 10 mM of buthionine S-R sulfoximine, which reduces the cellular non-protein sulfhydryl levels to less than 5% of control levels, significantly enhances the mutagenic incidence by cytoplasmic irradiation. Our results show, for the first time, that cytoplasmic traversal of mammalian cells by (-particles is mutagenic via a mechanism different from that of nuclear traversal, probably involving oxyradicals.