Borovitskaya A E, Evtushenko V I, Sabol S L
Laboratory of Biochemical Genetics, National Heart, Lung, and Blood Institute, Bethesda, MD 20892, USA.
Brain Res Mol Brain Res. 1996 Jan;35(1-2):19-30. doi: 10.1016/0169-328x(95)00177-t.
Low-dose ionizing irradiation of 16-18-day pregnant rats rapidly kills stem cells in the fetal forebrain. We have examined gamma-irradiated 17-day fetal rat brain tissue for molecular characteristics of apoptosis and changes in levels of mRNAs relevant to apoptosis. In many forebrain cells radiation elicits within 5 h nuclear condensation and fragmentation consistent with apoptosis. An electrophoretic DNA ladder indicative of internucleosomal chromatin cleavage was prominent within 3 h after irradiation. Pretreatment of pregnant rats with cycloheximide, or pretreatment of dissociated fetal brain cells in culture with actinomycin D, abolished the radiation-induced internucleosomal DNA fragmentation, demonstrating requirements for protein and RNA synthesis. Irradiation dramatically increased the level of the p53 transcription factor and the abundances of mRNAs coding for the cell-cycle inhibitor p21/Waf-1/Cip-1 and the AP-1-associated transcription factors Fos and JunB. Irradiation moderately increased the level of mRNA for the positive apoptosis regulator Bax. In contrast, irradiation reduced by 50-70% the abundances of most other mRNAs tested, including those for housekeeping proteins, p53, Jun, Myc, interleukin-1-beta-converting enzyme, and the negative apoptosis regulators Bcl-2 and Bcl-xL. These results indicate that radiation-elicited apoptosis of fetal brain cells is associated with activation of the p53 system, probable increases in AP-1 Fos/JunB heterodimers, and an increased ratio of Bax to Bcl-2 + Bcl-xL.
对怀孕16 - 18天的大鼠进行低剂量电离辐射会迅速杀死胎儿前脑的干细胞。我们检测了经γ射线辐照的17天龄胎鼠脑组织，以了解细胞凋亡的分子特征以及与细胞凋亡相关的mRNA水平变化。在许多前脑细胞中，辐射在5小时内引发核浓缩和碎片化，这与细胞凋亡一致。辐照后3小时内，一条指示核小体间染色质裂解的电泳DNA梯带很明显。用环己酰亚胺预处理怀孕大鼠，或在培养中用放线菌素D预处理解离的胎脑细胞，可消除辐射诱导的核小体间DNA碎片化，这表明蛋白质和RNA合成是必需的。辐照显著增加了p53转录因子的水平以及编码细胞周期抑制剂p21/Waf-1/Cip-1和与AP-1相关的转录因子Fos和JunB的mRNA丰度。辐照适度增加了正向细胞凋亡调节因子Bax的mRNA水平。相比之下，辐照使大多数其他测试的mRNA丰度降低了50 - 70%，包括管家蛋白、p53、Jun、Myc、白细胞介素-1-β转换酶以及负向细胞凋亡调节因子Bcl-2和Bcl-xL的mRNA。这些结果表明，辐射诱导的胎脑细胞凋亡与p53系统的激活、AP-1 Fos/JunB异二聚体可能增加以及Bax与Bcl-2 + Bcl-xL的比例增加有关。
