Interleukin-1β/Radiation-inducible/Gene expression/Nuclear protein/Electrophoretic mobility-shift assay. Immediately after X-irradiation, monocytic cells can express the gene for interleukin (IL)-1β, which enhances inflammation and contributes to radioprotection in mice. In order to analyze the mechanism(s) for the immediate-early induction of IL-1β after X-irradiation at 20 Gy in cultured murine macrophages, we examined the molecules that bound to the DNA fragments corresponding to the

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... region of 10 kb of the mouse IL-1β gene using an electrophoretic mobility-shift assay. Three DNA fragments corresponding to the 8,500, 8,000 and 2,500 bases upstream of the gene showed an unique binding site with the nuclear extract. Specific binding activity with these DNA fragments was observed in the nuclear extract from non-irradiated cells, and disappeared upon a pretreatment of the extract with proteinase K. The binding activity was not detected in the nuclear extract from irradiated cells. This shows that protein(s) specifically binding to the farupstream regions of the IL-1β gene disappear immediately after X-irradiation in the nuclei of macrophage cells, and that the event is potentially related to the immediate-early response of IL-1β gene expression.