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To understand the effects of ionizing radiation on the production of IL-1 alpha in vivo within a hematopoietic organ, we evaluated acute changes in splenic IL-1 alpha mRNA and IL-1 alpha protein after exposing B6D2F1 mice to lethal and sublethal 60Co radiation. Results suggest that in vivo, ionizing radiation induces a time- and dose-dependent accumulation of IL-1 alpha mRNA in the mouse spleen after exposure to gamma radiation. Time-dependent increases in the level of IL-1 alpha protein were also observed, although the magnitude of increased protein expression did not complement the magnitude of the accumulation of the message. Selective concentration of cells producing IL-1 alpha does not appear to account completely for the increase in splenic IL-1 alpha mRNA observed in this in vivo system.

Previous work by our group and others has shown the modulation of human immunodeficiency virus (HIV) promoter or long terminal repeat (LTR) after exposure to neutrons and ultraviolet radiations. Using HeLa cells stably transfected with a construct containing the chloramphenicol acetyl transferase (CAT) gene, the transcription of which is mediated by the HIV-LTR, we designed experiments to examine the effects of exposure to different types of radiation (such as gamma rays, ultraviolet and sunlight irradiations, electromagnetic fields and microwaves) on HIV-LTR-driven expression of CAT. These results demonstrated ultraviolet-light-induced transcription from the HIV promoter, as has been shown by others. Exposure to other DNA-damaging agents such as gamma rays and sunlight (with limited exposures) had no significant effect on transcription mediated by HIV-LTR, suggesting that induction of HIV is not mediated by just any type of DNA damage but rather may require specific types of DNA damage. Microwaves did not cause cell killing when cells in culture were exposed in high volumes of medium, and the same cells showed no changes in expression. When microwave exposure was carried out in low volumes of medium (so that excessive heat was generated) induction of HIV-LTR transcription (as assayed by CAT activity) was evident. Electromagnetic field exposures had no effect on expression of HIV-LTR. These results demonstrate that not all types of radiation and not all DNA-damaging agents are capable of inducing HIV. We hypothesize that induction of HIV transcription may be mediated by several different signals after exposure to radiation.

Studies were designed to identify genes induced in fibroblasts after exposure to low-dose neutron radiation but not after gamma rays. Our past work had shown similar modulation of transcripts for alpha-tubulin, beta- and gamma-actins, ornithine decarboxylase and interleukin 1 after exposure to either neutrons or gamma rays. However, differences in the expression of beta-protein kinase C and c-fos genes were observed, with both being induced after exposure to gamma rays but not neutrons. Recently we have identified two genes that are induced after exposure to neutrons but not gamma rays: Rp-8 (a gene associated with apoptosis) and the long terminal repeat (LTR) of the human immunodeficiency virus (HIV). Induction of Rp-8 mRNA was demonstrated in Syrian hamster embryo (SHE) fibroblasts and was found to be induced in cells exposed to neutrons administered at low (0.005 Gy/min) and high dose rate (0.12 Gy/min). No induction of other genes associated with apoptosis such as Rp-2, bcl-2 and Tcl-30 was observed. The induction of transcription from the LTR of HIV was demonstrated in HeLa cells bearing a transfected construct of the chloramphenicol acetyl transferase (CAT) gene driven by the HIV-LTR promoter. Measurements of CAT activity and CAT transcripts after irradiation demonstrated an unresponsiveness to gamma rays over a broad range of doses (0.1-3 Gy). Twofold induction of the HIV-LTR was detected after exposure to neutrons (0.48 Gy) administered at low (0.05 Gy/min) but not high (0.12 Gy/min) dose rates. Ultraviolet-mediated HIV-LTR induction, however, was inhibited by exposure to low-dose-rate neutron irradiation. These results are interesting in light of reports that Rp-8 is induced during apoptosis and that HIV causes apoptosis.

Experiments were designed to examine the effects of radiation quality on specific gene expression within the first 3 h following radiation exposure in Syrian hamster embryo (SHE) cells. Preliminary work demonstrated the induction of c-fos and alpha-interferon genes following exposure to low-linear-energy-transfer (low-LET) radiations (X rays or gamma rays). More detailed experiments revealed induction of c-fos mRNA within the first 3 h following exposure to either X rays (75 cGy) or gamma rays (90 cGy). We could not detect induction of c-fos following exposure of SHE cells to fission-spectrum neutrons (high-LET) from the JANUS reactor administered at either high (12 cGy/min) or low (0.5 cGy/min) dose rates. Expression of alpha-interferon mRNA was similarly induced by low-LET radiations but only modestly by JANUS neutrons. The induction by gamma rays was dose-dependent, while induction by neutrons was specific for low doses and low dose rates. These experiments demonstrate the differential gene inductive response of cells following exposure to high- and low-LET radiations. These experiments suggest that these different qualities of ionizing radiation may have different mechanisms for inducing many of the cellular consequences of radiation exposure, such as cell survival and cell transformation.

Survival parameters and immediate DNA damage induced by 60Co gamma rays, 50-kVp X rays, and Janus fission-spectrum neutrons in human epithelial P3 cells (derived from an embryonic teratocarcinoma) are compared with those for Chinese hamster lung V79 cells. DNA damage caused by X and gamma irradiation, measured by alkaline elution methods, is the same in both cell types, whereas the P3 cells are about two times more sensitive (as measured by Do ratios of the final survival curve slope) to the lethal effects of these radiations than are the V79 cells. Human P3 cells are also more sensitive to the lethal effects of fission-spectrum neutrons than V79 cells. Survival experiments with split radiation doses and hypertonic salt treatment indicate that both P3 cells and V79 cells can recover from radiation-induced damage efficiently.

Survival parameters and immediate DNA damage induced by 60Co gamma rays, 50-kVp X rays, and Janus fission-spectrum neutrons in human epithelial P3 cells (derived from an embryonic teratocarcinoma) are compared with those for Chinese hamster lung V79 cells. DNA damage caused by X and gamma irradiation, measured by alkaline elution methods, is the same in both cell types, whereas the P3 cells are about two times more sensitive (as measured by Do ratios of the final survival curve slope) to the lethal effects of these radiations than are the V79 cells. Human P3 cells are also more sensitive to the lethal effects of fission-spectrum neutrons than V79 cells. Survival experiments with split radiation doses and hypertonic salt treatment indicate that both P3 cells and V79 cells can recover from radiation-induced damage efficiently.