DNA Damage Responses in Cell Cycle G₂ Phase and Mitosis - Tracking and Targeting

Abstract

Background: In order to determine temporal responses of cell cycle populations to DNA damage, a rational combination of cell cycle analyses is critical. Moreover, the targeting of cell cycle checkpoint responses may modify the cytotoxic effect of DNA damage. Materials and Methods: The characteristics of cell cycle populations (DNA content, cell cycle transitioning of S phase cells and size of mitotic cell fraction within the total G₂/M phase population) in HeLa cells exposed to ionizing radiation were analyzed using three individual flow cytometry-based assays. The potential radiosensitization from inhibiting DNA damage responses was assessed by the colony formation assay. Results: Irradiation resulted in an initial accumulation of S phase cells in G₂ phase, from which the arrested cells were subsequently released to enter mitosis. Upon drug inhibition of G₂ checkpoint signaling or mitotic progression, the cytotoxic effect of ionizing radiation on the HeLa cells was amplified. Conclusion: DNA damage-induced cell cycle responses, analyzed by selected cytometry assays and modified by specific targeting, might contribute to an understanding of how to improve radiotherapy outcome.