Correlations between Radiation-induced Double Strand Breaks and Cell Cycle Checkpoints in X-irradiated NIH/3T3 Fibroblasts

Abstract

Background: To better understand the relationship between the formation of radiation-induced DNA double strand breaks (DSB) and cell cycle checkpoint activation, studies were conducted in the NIH/3T3 fibroblast cell line in order to establish correlations between the temporal appearance of γ-H2AX foci (a DSB) and the expression of the cell cycle regulatory proteins, the cyclins, and their cyclin kinase inhibitor, p21. Materials and Methods: Immunocytochemistry was used to determine the expression of cyclin E, A, B1, p21, and the generation of DSB in NIH/3T3 cells exposed to 2 or 4 Gy X-irradiation. Results and Discussion: The data suggest that the G₁/S- and S-phase delay (cyclin E and cyclin A protein levels) are dependent on the dose of radiation while the G₂/M (cyclin B1 protein levels) delay is dependent on the quantity of DSB sustained by the irradiated cell.