Correlations between radiation-induced double strand breaks and cell cycle checkpoints in X-irradiated NIH/3T3 fibroblasts.

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 gamma-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.