title: Induced expression of the IER5 gene by gamma-ray irradiation and its involvement in cell cycle checkpoint control and survival.
abstract: 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 15 Gy 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 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 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 2 h and 12-24 h 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 6 Gy, but barely affected the sensitivity of cells at 8 Gy. 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.
authors.affiliation: Biomedical Engineering School, Capital Medical University, Beijing, People's Republic of China.
authors.forename: Ku-Ke
authors.initials: KK
authors.lastname: Ding
authors.forename: Zeng-Fu
authors.initials: ZF
authors.lastname: Shang
authors.forename: Chuan
authors.initials: C
authors.lastname: Hao
authors.forename: Qin-Zhi
authors.initials: QZ
authors.lastname: Xu
authors.forename: Jing-Jing
authors.initials: JJ
authors.lastname: Shen
authors.forename: Chuan-Jie
authors.initials: CJ
authors.lastname: Yang
authors.forename: Yue-Hua
authors.initials: YH
authors.lastname: Xie
authors.forename: Cha
authors.initials: C
authors.lastname: Qiao
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Xu
authors.forename: Ping-Kun
authors.initials: PK
authors.lastname: Zhou
mesh_terms: D002453:Cell Cycle / Q000528:radiation effects*; D002460:Cell Line; D049109:Cell Proliferation; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D005720:Gamma Rays; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D017874:Immediate-Early Proteins / Q000096:biosynthesis*; D008214:Lymphocytes / Q000528:radiation effects; D009687:Nuclear Proteins / Q000096:biosynthesis*; D034741:RNA, Small Interfering / Q000378:metabolism; D011836:Radiation Tolerance; D013997:Time Factors; D014162:Transfection
chemical_list: C118926:IER5 protein, human; D017874:Immediate-Early Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering