The inhibition of p21 on irradiation-induced apoptosis in EL-4 cells.

Abstract

e13558 Background: To elucidate the effect of p21 on ionizing radiation-induced apoptosis in EL-4 cells. Methods: In EL-4 cells, RT-PCR, immunocytochemistry and flow cytometry (FCM) were used to analyze the changes in the expression of p21 with time and doses caused by ionizing radiation; RNAi was used to silence the expression of p21 in EL-4 cells; FCM was applied to analyze the distribution of cell cycle,the number of the chromosome and the apoptosis in wild or p21-silencing EL-4 cells exposed to X-rays. Results: In EL-4 cells, p21 protein level was markedly increased at 8 ~ 72 h after exposure in 4.0 Gy of X-ray in vitro (p<0.01), as well as exposed in 1.0 ~ 4.0 Gy of X-ray at 24 h in vitro (p<0.05). Results of time-course experiments showed that, in EL-4 cells exposed to 4.0 Gy X-rays, the percentage in G0/G1 phase increased while that in S phase decreased, significantly different with the sham-irradiated groups (p<0.05), during 8-48h after exposure; the percentage of diploid cells increased significantly during 8-48 h (p<0.01), and the percentage of tetraploid and octoploid cells decreased significantly at 2 h and 8 h (p<0.05); the percentage of apoptosis during 2-72 h increased significantly (p<0.05-p<0.01). Compared with wild EL-4 cells, in p21-silencing EL-4 cells, the distribution of cell cycle had no apparent difference; the percentage of diploid cells decreased significantly and the percentage of octoploid cells increased significantly (p<0.01); the percentage of apoptosis increased significantly (p<0.05). Conclusions: p21 inhibited the apoptosis induced by ionizing radiation in EL-4 cells.