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

胸腺细胞对辐射高度敏感，在低剂量照射后数小时内出现间期死亡。最近，我们有证据表明，辐射引起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，研究了细胞死亡的机制。用1kr x射线辐照的大鼠胸腺细胞经红素B染色判断为期间死亡，并伴有离散细胞大小减小和DNA降解。放线菌素D和环己亚胺等RNA和蛋白质合成抑制剂完全阻断了细胞的死亡和这些变化。这些结果有力地表明，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，在10氪照射后，观察到细胞逐渐肿胀，甚至出现特征性的坏死变化，环己亚胺已不能再阻止细胞死亡。因此，高剂量辐射可能破坏了细胞凋亡所需的某些蛋白质合成过程。结果，在大剂量辐照后，细胞不是死于凋亡，而是死于坏死。用Percoll密度梯度法分离活细胞和死细胞，用二维ge%i电泳法检测可能参与凋亡的蛋白。与活细胞相比，我们可以检测到27 kDa蛋白的特异性出现和29 kDa蛋白在死细胞中的消失。有关这些蛋白质的研究正在进行中。

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.