Mechanisms of radiation-induced interphase death of thymocytes expressed as apoptosis

胸腺细胞对辐射高度敏感，在低剂量辐射后数小时内出现间期死亡。近年来，有证据表明，辐射诱导的胸腺细胞间期死亡是一种程序性死亡，称为“凋亡”。在本研究中，细胞死亡的机制进行了研究，在体外大鼠胸腺细胞照射1 KR X射线发生间期死亡，通过红B染色判断，伴随着离散的细胞大小减少和DNA降解。RNA和蛋白质合成抑制剂放线菌素D和放线菌酮可完全阻断细胞的死亡和上述变化，这些结果表明细胞死亡不是一个被动的事件，而是一个主动的过程，需要特定的RNA和蛋白质的程序化合成。然而，10KR照射后，细胞逐渐肿胀，甚至出现坏死的特征性变化，而环己酰亚胺不能阻止细胞死亡。因此，可能是高剂量照射破坏了细胞凋亡所需的某些蛋白质合成过程。结果，细胞不是通过凋亡而死亡的。为了检测与儿童下垂有关的蛋白质，采用Percoll密度梯度分离法对活细胞和死细胞蛋白质进行双向电泳。与活细胞的蛋白质比较，我们可以检测到27kDa蛋白在死细胞中的特异性出现和29kDa蛋白的消失，对这些蛋白的研究正在进行中。

Thymocytes are highly radiosensitive and show interphase death within a few hours after low doses of irradiation. recently,we obtained evidence to indicate that the radiation-induced interphse death of thymocytes is a king of programmed death named"apoptosis". In the present study,the mechanisms underlying the cell death were investigated.Rat thymocytes irradiated in vitro with 1 KR X-rays underwent interphase death,judged by erythrosin B staining,accompanying discrete cell size reduction and DNA degradation. The cell death as well as these changes were completely blocked by inhibitors of RNA and protein synthesis such as actinomycin D and cycloheximide.These results suggest strongly that the cell death is not a passive event,but an active process requiring the programmed synthesis of specific RNA and proteins. After 10 KR irradiation, however, gradual swelling of cells, oen of the characteristic changes of necrosis,was observed and cell death could no more be prevented by cyckoheximide.It is possible,therefore,that some process of protein synthesis reauired to develop apotosis was damaged by the high doses irradiation.As a result cells die not by apoptosis,but by necrosis after massive doses irradiation.For detection of proteins which might perticipate in paoptosis,two demensional ge%i elcrophoresis of the proteins of the viable and dead cells separated by Percoll density gradient was conducted. In comparison with the proteins of viable cells we could detect specific appearance of 27 kDa protein and disapearance of 29 kDa protein in the dead cells.Investigations concerning these proteins are now in progress.