title: Dose and dose-rate effects of low-dose ionizing radiation on activation of Trp53 in immortalized murine cells.
abstract: A derivative of immortalized murine NIH/PG13Luc cells stably transfected with a Trp53-dependent luciferase reporter plasmid was used to study the transcriptional activity of Trp53 in response to radiation. The cell line was sensitive enough to detect the response of Trp53 to 0.2 cGy of (60)Co gamma radiation. To examine the biological effects of low-dose-rate (60)Co gamma radiation (from 0.1-10 cGy/h), we have analyzed the cell cycle, Trp53 transcriptional activity, and gene expression profiles of control and treated cells. Microarray analysis revealed up-regulation of six Trp53-mediated genes (Cdkn1a/ p21, Mdm2, Sip27, Ccng1/cyclin G1, Ei24/Pig8 and Dinb/ Polk) after exposure of cells to low-dose-rate radiation for 72 h. Using real-time PCR, a significant elevation in the expression of Ccng1/cyclin G1, Mdm2 and Cdkn1A/p21 was observed with low-dose-rate irradiation at dose rates over 5 cGy/ h. A dose-rate dependence was also observed for these three Trp53-mediated genes. The expression of Ccng1/cyclin G1 at high dose rates of gamma rays was higher than that for low dose rate. However, the expression of Mdm2 for low-dose-rate gamma rays was higher than for the high dose rate. Cells irradiated at low dose rates of 0.1 cGy/h and 1 cGy/h underwent G(1)-phase arrest. Furthermore, G(2)-phase growth arrest was observed in cells irradiated at the low dose rates of 5 cGy/h and 10 cGy/h, which correlated with Trp53-mediated Ccng1/cyclin G1 up-regulation. These results show that cellular response to radiation depended on the dose rate used; i.e., the responses seen at dose rates from 0.1-1 cGy/h were different from those observed at dose rates over 5 cGy/h.
authors.affiliation: Department of Radiobiology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan. sagihara@ies.or.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Sugihara
authors.forename: Junji
authors.initials: J
authors.lastname: Magae
authors.forename: Renu
authors.initials: R
authors.lastname: Wadhwa
authors.forename: Sunil C
authors.initials: SC
authors.lastname: Kaul
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kawakami
authors.forename: Tsuneya
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Kimio
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000528:radiation effects; D002455:Cell Division / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005786:Gene Expression Regulation / Q000528:radiation effects*; D051379:Mice; D041681:NIH 3T3 Cells; D011829:Radiation Dosage; D011839:Radiation, Ionizing; D015533:Transcriptional Activation / Q000528:radiation effects*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism* / Q000528:radiation effects*
chemical_list: D016159:Tumor Suppressor Protein p53