Induced expression of the IER5 gene by g-ray irradiation and its involvement in cell cycle checkpoint control and survival

• Published in: Radiation and environmental biophysics 2009-04, Vol.48 (2), p.205-213
• Main Authors: Ding, Ku-Ke, Shang, Zeng-Fu, Hao, Chuan, Xu, Qin-Zhi, Shen, Jing-Jing, Yang, Chuan-Jie, Xie, Yue-Hua, Qiao, Cha, Wang, Yu, Xu, Li-Li, Zhou, Ping-Kun
• Format: Article
• Language: English
• ISSN: 0301-634X; 1432-2099
• DOI: 10.1007/s00411-009-0213-4

The immediate-early response gene 5 (IER5) was previously shown, using microarray analysis, to be upregulated by ionizing radiation. Here we further characterized the dose- and time-dependency of radiation-induced expression of IER5 at doses from 0.5 to 15Gy by quantitative real-time PCR analyses in HeLa cells and human lymphoblastoid AHH-1 cells. A radiation-induced increase in the IER5 mRNA level was evident 2h after irradiation with 2Gy in both cell lines. In AHH-1 cells the expression reached a peak at 4h and then quickly returned to the control level, while in HeLa cells the expression only remained increased for a short period of time at around 2h after irradiation before returning to the control. After high-dose irradiation (10Gy), the induction of the IER5 expression was lower and delayed in AHH-1 cells as compared with 2-Gy irradiated cells. In HeLa cells, at this dose, two peaks of increased expression were observed 2h and 12-24h post-irradiation, respectively. RNA interference technology was employed to silence the IER5 gene in HeLa cells. siRNA-mediated suppression of IER5 resulted in an increased proliferation of HeLa cells. Cell growth and survival analyses demonstrated that suppression of IER5 significantly increased the radioresistance of HeLa cells to radiation doses of up to 6Gy, but barely affected the sensitivity of cells at 8Gy. Moreover, suppression of IER5 potentiated radiation-induced arrest at the G2-M transition and led to an increase in the fraction of S phase cells. Taken together, we propose that the early radiation-induced expression of IER5 affects the radiosensitivity via disturbing radiation-induced cell cycle checkpoints.