24h Post-irradiation Research Articles

Differential modulation of interleukin‐1α (IL‐1α) and interleukin‐1β(IL‐1β in human epidermal keratinocytes by UVB

Conflicting reports exist concerning ultraviolet-B (UVB) effects on keratinocyte (KC) interleukin-1 (IL-1) expression. To clarify the modulatory effects of UVB on IL-1, the following study was undertaken. Normal human epidermal KCs cultured in a standard low Ca2+ and serum-free medium were irradiated in quiescent phase with UVB. In this study, we used semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to determine the mRNA level of interleukin-1 alpha (IL-1 alpha) and interleukin-1 beta (IL-1 beta). After exposure to 100 or 300 J/m2 UVB, a transient increase in mRNA levels was observed within 1 hour for IL-1 alpha and 3 to 6 h for IL-1 beta. Following this transient induction, mRNA levels for both IL-1 alpha and IL-1 beta returned to steady-state levels after 100 J/m2. After 300 J/m2 irradiation, IL-1 alpha and IL-1 beta levels were downregulated compared to unirradiated cultures at 24-h post-irradiation. The half-life for IL-1 alpha and IL-1 beta was estimated using actinomycin D treatment. Both IL-1 alpha and IL-1 beta mRNAs half-lives (t1/2) decreased faster in irradiated cells (t1/2 = 30 minutes for IL-1 alpha and 2 h for IL-1 beta) compared to unirradiated cells (t1/2 = 1 h and 4 h, respectively). These results suggest that IL-1 alpha and IL-1 beta mRNA expression are differentially regulated by UVB. In contrast to down-regulation of mRNA levels, a significant increase in IL-1 alpha protein levels, measured by ELISA, was observed in culture supernatants from 6 h to 24 h after 300 J/m2 UVB irradiation. Cycloheximide treatment did not abrogate this increase in IL-1 alpha protein level. Since this dose of UVB irradiation decreased the stability of IL-1 alpha and IL-1 beta mRNA, this suggests that the release of IL-1 alpha after UVB irradiation was due to leakage from UVB-damaged cells and not from de novo protein synthesis.

Radiosensitivity in ataxia-telangiectasia: anomalies in radiation-induced cell cycle delay.

A number of anomalies have been described in the progression of ataxia-telangiectasia (AT) cells through the cell cycle post-irradiation. Some uncertainty still exists as to whether AT cells show increased or reduced division delay after exposure to ionizing radiation. We have attempted to resolve the apparent inconsistencies that exist by investigating the effects of radiation on AT cells at various stages of the cell cycle. Specific labelling of S phase cells with 5-bromodeoxyuridine (BrdU) followed by irradiation caused a prolonged accumulation of these cells in G2/M phase with only 2-7% of AT cells progressing through to G1 24h post-irradiation. In contrast, 23-28% of control cells irradiated in S phase reached G1 by 24 h after irradiation. As observed previously with AT fibroblasts, AT lymphoblastoid cells irradiated in G1 phase did not experience a delay in entering S phase. After progressing through S phase these cells also were delayed in G2/M, but not to the same extent as irradiated S phase cells. On the other hand, when AT cells were irradiated in G2 phase they showed less delay initially in entry to mitosis and the subsequent G1 phase than did irradiated control cells. The overall results demonstrate that AT cells fail to show an initial delay in transitions between the G1/S and G2/M phases of the cell cycle and in progression through these phases post-irradiation, but in the long-term, after passage through S phase, they experience a prolonged delay in G2/M. Since several AT complementation groups are represented in this study, the cell cycle anomalies appear to be universal in AT. These results implicate deficiencies in control of cell cycle progression in the increased radiosensitivity and cancer predisposition in AT.

Radioprotective Effects in Mice by a Single Dose of Subcutaneous Administration of Cobaltous Chloride Post .GAMMA.-Rays Irradiation with a Sublethal Dose.

Radioprotective effects were investigated in mice which received subcutaneously a single dose of each inorganic metal: Co, Cu, Rb, Sr, Mo and W 24h post irradiation of 60Co γ-rays with a sublethal dose.The effects were observed in mice injected with Co at an optimum dosage of 20 mg/kg· body weight. Then to elucidate mechanisms of the effects, mice were injected with Co containing the radioactive tracer (60Co) following the radiation exposure, measured elimination of the radioactivity for 7 days, then sacrificed and divided to some tissues and organs. The radioactivity in whole body during this period resulted in a markedly higher retention than that for mice injected with [60Co] alone, as well as liver in the organs. These higher retentions appeared to be related to the radioprotective effects.

Comparison of γ-radiation-induced accumulation of ataxia telangiectasia and control cells in G2 phase

Recent reports from a number of laboratories have linked radiosensitivity in ataxia telangiectasia (A-T) to a large and prolonged block of some cells in G2 phase. Previous results from this laboratory, largely with one Epstein-Barr virus-transformed A-T lymphoblastoid cell line, presented evidence for a dramatic increase in the number of cells in G2 phase over controls during a 24-h period post irradiation. We describe here a study of the effect of γ-radiation on G2 phase delay in several A-T cell lines. Based on previous results with several cell lines 24 h post irradiation was selected as the optimum time to discriminate between G2 phase delay in control and A-T cells. All A-T homozygotes showed a significantly greater number of cells in G2 phase, 24 h post irradiation, than observed in controls. A more prolonged delay in G2 phase after irradiation was seen in different A-T cell types that included lymphoblastoid cells, fibroblasts and SV40-transformed fibroblasts. At the radiation dose used it was not possible to distinguish A-T heterozygotes from controls.