Increase of intracellular glutathione by low-dose gamma-ray irradiation is mediated by transcription factor AP-1 in RAW 264.7 cells.

The mechanism of the elevation of intracellular glutathione induced by low-dose gamma-rays was examined in RAW 264.7 cells. The expression of mRNA for gamma-glutamylcysteine synthetase (gamma-GCS) increased soon after gamma-ray (0.5 Gy) irradiation, and peaked between 3 h and 6 h post-irradiation. A dose of 0.25 to 0.5 Gy was optimum for induction of gamma-GCS mRNA expression at 3 h post-irradiation. The effect of inhibitors of activator protein-1 (AP-1) and nuclear factor kappaB (NF-kappaB) on the radiation-induced gamma-GCS gene expression was then examined. The induction of gamma-GCS mRNA expression was significantly suppressed when AP-1 DNA binding, but not NF-kappaB DNA binding, was inhibited. Finally, electrophoretic mobility shift assay showed that the low-dose radiation markedly increased the DNA binding of AP-1, but not NF-kappaB, soon after irradiation. These results suggest that the increase of glutathione levels in RAW 264.7 cells by low-dose gamma-ray irradiation is mediated by transcriptional regulation of the gamma-GCS gene, predominantly through the AP-1 binding site in its promoter.