ABSTRACT
Adaptive response (AR) and bystander effect are two important phenomena involved in biological responses to low doses of ionizing radiation (IR). Furthermore, there is a strong interest in better understanding the biological effects of high-LET radiation. We previously demonstrated the ability of low doses of X-rays to induce an AR to challenging heavy-ion radiation [8]. In this study, we assessed in vitro the ability of priming low doses (0.01Gy) of heavy-ion radiation to induce a similar AR to a subsequent challenging dose (1-4Gy) of high-LET IR (carbon-ion: 20 and 40keV/µm, neon-ion: 150keV/µm) in TK6, AHH-1 and NH32 cells. Our results showed that low doses of high-LET radiation can induce an AR characterized by lower mutation frequencies at hypoxanthine-guanine phosphoribosyl transferase locus and faster DNA repair kinetics, in cells expressing p53.
Subject(s)
Adaptation, Biological , Heavy Ions , Linear Energy Transfer , Lymphocytes/radiation effects , Mutation , Cell Line , DNA Repair , Humans , Hypoxanthine Phosphoribosyltransferase/genetics , Neon , Radiation Dosage , Radiation, IonizingABSTRACT
The ability of cells to adapt low-dose or low-dose rate radiation is well known. High-LET radiation has unique characteristics, and the data concerning low doses effects and high-LET radiation remain fragmented. In this study, we assessed in vitro the ability of low doses of X-rays to induce an adaptive response (AR) to a subsequent challenging dose of heavy-ion radiation. Lymphoblastoid cells (TK6, AHH-1, NH32) were exposed to priming 0.02-0.1Gy X-rays, followed 6h later by challenging 1Gy heavy-ion radiation (carbon-ion: 20 and 40keV/µm, neon-ion: 150keV/µm). Pre-exposure of p53-competent cells resulted in decreased mutation frequencies at hypoxanthine-guanine phosphoribosyl transferase locus and different H2AX phosphorylation kinetics, as compared to cells exposed to challenging radiation alone. This phenomenon did not seem to be linked with cell cycle effects or radiation-induced apoptosis. Taken together, our results suggested the existence of an AR to mutagenic effects of heavy-ion radiation in lymphoblastoid cells and the involvement of double-strand break repair mechanisms.
Subject(s)
Adaptation, Physiological/radiation effects , Linear Energy Transfer , Lymphocytes/radiation effects , Mutation/radiation effects , Apoptosis/radiation effects , Cell Cycle/radiation effects , Cell Line , Dose-Response Relationship, Radiation , Histones/metabolism , Humans , Hypoxanthine Phosphoribosyltransferase/genetics , Kinetics , Lymphocytes/cytology , Lymphocytes/metabolism , Phosphorylation/radiation effects , Radiation Tolerance/radiation effects , Time FactorsABSTRACT
Measuring global gene expression using cDNA or oligonucleotide microarrays is an effective approach to understanding the complex mechanisms of the effects of radiation. However, few studies have been carried out that investigate gene expression in vivo after prolonged exposure to low-dose-rate radiation. In this study, C57BL/6J mice were continuously irradiated with gamma-rays for 485 days at dose-rates of 0.032-13 microGy/min. Gene expression profiles in the kidney and testis from irradiated and unirradiated mice were analyzed, and differentially expressed genes were identified. A combination of pathway analysis and hierarchical clustering of differentially expressed genes revealed that expression of genes involved in mitochondrial oxidative phosphorylation was elevated in the kidney after irradiation at the dose-rates of 0.65 microGy/min and 13 microGy/min. Expression of cell cycle-associated genes was not profoundly modulated in the kidney, in contrast to the response to acute irradiation, suggesting a threshold in the dose-rate for modulation of the expression of cell cycle-related genes in vivo following exposure to radiation. We demonstrated that changes to the gene expression profile in the testis were largely different from those in the kidney. The Gene Ontology categories "DNA metabolism", "response to DNA damage" and "DNA replication" overlapped significantly with the clusters of genes whose expression decreased with an increase in the dose-rate to the testis. These observations provide a fundamental insight into the organ-specific responses to low-dose-rate radiation.
Subject(s)
Gamma Rays , Gene Expression Regulation , Kidney/metabolism , Radiation , Testis/metabolism , Animals , Dose-Response Relationship, Radiation , Male , Mice , Mice, Inbred C57BL , Microarray AnalysisABSTRACT
CDKN1A is a cyclin-dependent kinase inhibitor that plays a critical role in cell cycle checkpoint regulation. It is transcriptionally induced by TP53 (p53) following exposure to ionizing radiation (IR). Induction of CDKN1A after irradiation is closely related to IR-sensitivity of tumor cells, but the underlying mechanisms remain obscure because conventional reporter gene systems respond poorly to IR unless hyperlethal doses are used. Here, we performed a promoter analysis of the CDKN1A gene following irradiation with clinically relevant doses of IR using the adeno-associated virus-mediated reporter system which we have recently shown to be highly responsive to IR. We demonstrate that there are regulatory elements at -1.1 kb, -1.4 kb, and -1.8 kb, and deletion of these elements attenuate induction of the CDKN1A gene promoter in response to 0.2-2.0 Gy of IR. EMSA and ChIP assays showed that Oct-1 binds constitutively to the elements at -1.1 kb and -1.8 kb. Functional involvement of Oct-1 was confirmed by RNA interference targeting the Oct-1 gene, which suppressed both the basal and IR-inducible components of the CDKN1A expression. Thus, our results reveal that Oct-1 is crucial to the TP53-mediated regulation of the CDKN1A gene promoter following exposure to clinically relevant doses of IR.
