The Effect Of Early G2/M Checkpoint On Low-dose Hyper-radiosensitivity In Human Adenocarcinoma Cell Line A549

Objective: The aims of this study were to observe whether low-dose radiationsensitivity could be increased by synchronization in human lung adenocarcinoma cellline A549and then characterize the effect of the early G2/M checkpoint on G2-phasepopulations..Methods: HRS-positive cells A549were used. A synchronization protocol withaphidicolin was performed to enrich the proportion of cells in the G2phase of the cellcycle. For the clonogenic survival assay, both asynchronous and G2-enrichedpopulations of A549cells were irradiated with single low-dose X-irradiation. Then theclonogenic survival data were fitted to MIRM model. Assessment ofanti–phospho-histone H3(Ser10) staining by flow cytometry to examine the cellcycle progression of irradiated G2cells. Measuring the γ-H2AX foci number byimmunofluorescence to evaluating the efficiency of DNA repair.Results: Asynchronous populations of A549cells were confirmed to exhibit HRSand amplified in G2phase–enriched populations. The dose response pattern of the early G2/M checkpoint corresponded with the transition in the survival response fromHRS to IRR. The early G2/M checkpoint of G2-phase A549cells to be activated at athreshold dose above0.4Gy, a failure to activate this checkpoint was concordant withlow-dose hyper-radiosensitivity. A threshold level of about15DSBs (double strandbreaks) was needed to efficiently initiate and maintain the early G2/M checkpoint. AsDSB repair proceeded, cell cycle progression was resumed when the remaining DSBsfell below this critical threshold.Conclusions: Low-dose hyper-radiasensitivity could be enhanced bysynchronization；There was a threshold dose to activate the early G2/M checkpoint ofG2-phase A549cells; A threshold level of DNA damage was needed to initiate andmaintain the early G2/M checkpoint.