Host: The Japan Radiation Research Society
Genomic instability has been commonly observed in various tumor cells and is considered the earliest cellular event in the process of carcinogenesis. Although genomic instability can be induced by ionizing radiation the molecular mechanisms underlying this process are poorly understood. Cell cycle checkpoints play a key role in cell survival following DNA damage. The failures of DNA repair and cell cycle regulation in response to DNA damage are thought to be important factors in the early stages of genomic instability. Several genes associated with DNA damage repair and cell cycle regulation are also related to radiation susceptibility. By a large-scale expression profiling of 15 human cell lines and three mouse strains having varying degrees of susceptibility to ionizing radiation, we identified 200 genes correlated with radiation susceptibility. We constructed an shRNA library of these 200 genes. We screened this library using 96-well format cell proliferation assay based on loss of function analysis, after X-irradiation. We identified 12 genes involved in radiation susceptibility. Eight of the 12 genes have been reported to directly or potentially regulate cell cycle, and biological functions of remaining four genes have not been reported. We then performed cell cycle analysis of cells transfected with shRNA vectors against these four genes following X-irradiation, and found that knockdown cells of one of these 4 genes did not accumulate in G2/M phase. This result suggests that this gene is associated with the G2/M checkpoint after DNA damage. Further study of the 12 radiation susceptibility genes identified in this screen may help to elucidate the molecular mechanisms of cell cycle progression, and to develop new radiation sensitizing agents for radiotherapy.
