Protein Biosynthesis in Low Dose Ionizing Radiation-Adapted Human Melanoma Cells

Adaptive responses induced by low dose γ-ray irradiation in human melanoma cells were examined using a clonogenic assay. Survival fractions were significantly increased in cells irradiated with low dose γ-rays then 4 hrs later with high dose γ-ray as compared to cells irradiated only with high dose γ-rays. When low dose irradiation was given 20 hrs prior to high dose irradiation, however, no adaptive response was induced. Changes in protein biosynthesis in human melanoma cells were observed under the same conditions. Significant changes in protein biosynthesis occurred in the nuclear and membrane proteins of cells first irradiated with a low dose then a high dose of γ-rays after 4 hrs. No such changes were found in cells irradiated with low dose γ-rays 20 hrs prior to high dose irradiation, consistent with the results of the clonogenic assay. Our findings suggest that prior treatment with low dose γ-rays induces an adaptive response that has a significant effect on the induction of the nuclear and membrane protein biosynthesis caused by high dose γ-ray irradiation of human melanoma cells.