Induction and quantification of γ-H2AX foci following low and high LET-irradiation

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Abstract
Purpose: To investigate quantitatively the induction and rejoining of DNA double strand breaks (DSB) in V79-4 and xrs-5 Chinese hamster cells and HF19 human fibroblast cells, using the phosphorylation of the histone protein H2AX (γ-H2AX) as an indicator of DSB, exposed to low doses of either low linear energy transfer (LET) 60Co γ-rays or high LET α-particles. Materials and methods: Cells were irradiated with low or high LET (20 – 2000 mGy). The γ-H2AX foci were detected using immunohistochemistry and quantified by image analysis. Results: The number of DSB determined 30 min post γ-irradiation at 37°C is 12.2 (±1.5), 13.5 (±1.6) and 19.1 (±1.7) foci/cell/Gy for V79-4, xrs-5 and HF19 cells respectively, comparable with levels detected in V79-4 cells using pulse field gel electrophoresis. 6 h post γ-irradiation, γ-H2AX foci levels in V79-4 and HF19 cells approach control levels but remain higher in DSB repair deficient xrs-5 cells. γ-H2AX foci levels remain significantly higher than controls at 6 h in α-irradiated cells. Conclusions: γ-radiation and α-radiation induced the phosphorylation of H2AX in response to DSB at low doses; the variation in the rate of dephosphorylation of induced foci are dependent both on radiation quality and cell characteristics.