Induced expression of the IER5 gene by γ-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
• Subjects: Biological and Medical Physics; Biophysics; Cell Cycle - radiation effects; Cell Line; Cell Proliferation; Dose-Response Relationship, Radiation; Ecosystems; Effects of Radiation/Radiation Protection; Environmental Physics; Flow Cytometry; Gamma Rays; Gene Expression Regulation; HeLa Cells; Humans; Immediate-Early Proteins - biosynthesis; Lymphocytes - radiation effects; Monitoring/Environmental Analysis; Nuclear Proteins - biosynthesis; Original Paper; Physics; Physics and Astronomy; Radiation Tolerance; RNA, Small Interfering - metabolism; Time Factors; Transfection
• ISSN: 0301-634X; 1432-2099
• DOI: 10.1007/s00411-009-0213-4

The immediate-early response gene 5 ( IER 5) 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 IER 5 at doses from 0.5 to 15 Gy by quantitative real-time PCR analyses in HeLa cells and human lymphoblastoid AHH-1 cells. A radiation-induced increase in the IER 5 mRNA level was evident 2 h after irradiation with 2 Gy in both cell lines. In AHH-1 cells the expression reached a peak at 4 h 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 2 h after irradiation before returning to the control. After high-dose irradiation (10 Gy), the induction of the IER 5 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 2 h and 12–24 h post-irradiation, respectively. RNA interference technology was employed to silence the IER 5 gene in HeLa cells. siRNA-mediated suppression of IER 5 resulted in an increased proliferation of HeLa cells. Cell growth and survival analyses demonstrated that suppression of IER 5 significantly increased the radioresistance of HeLa cells to radiation doses of up to 6 Gy, but barely affected the sensitivity of cells at 8 Gy. Moreover, suppression of IER 5 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 IER 5 affects the radiosensitivity via disturbing radiation-induced cell cycle checkpoints.