gamma-radiation-induced G(2) delay, apoptosis, and p53 response as potential susceptibility markers for lung cancer

gamma -Radiation results in cell cycle arrest and apoptosis in a wide varie ty of cells. Cell cycle arrest provides time for the cell to repair damaged DNA before entering the next phase of the cycle. If the damage is severe a nd cannot be repaired, the cells undergo apoptosis. However, if the damaged cells continue to grow without repair or apoptosis, then carcinogenic tran sformation may occur. We hypothesized that individuals with inherited disru ption in cell cycle control and/or apoptosis and/or DNA repair may be susce ptible to lung cancer development. The cells from susceptible individuals w ould have a shorter G(2) period and less apoptosis compared with cells from normal individuals upon exposure to gamma -radiation. To test this hypothe sis, the following methods were used: (a) fluorescence-activated cell sorti ng method was used to measure apoptosis and G(2) cell cycle delay; (b) the ELISA method was used to measure p53 protein expression levels in these cel l lines; and (c) gamma -radiation-induced chromatid breaks were counted as a marker for DNA damage or repair. Next, gamma -radiation-induced G(2) dela y and apoptosis were tested in three lymphoblastoid cell lines to determine the dose response effect and optimal time points of gamma -radiation. Fina lly, these assays were tested in lymphoblastoid cell tines from 30 lung can cer patients and 22 healthy controls. We found a dose-response relationship for gamma -radiation-induced G(2) delay and apoptosis. The optimal time po ints to detect differential G(2) delay and apoptotic index were 10 h and 48 h after gamma -radiation, respectively. The mean G(2) delay was 22.5 % +/- 10.5 % for the control cell tines and 14.71 % +/- 8.8 % for case cell line s (P < 0.01). The mean apoptotic index was 20.4% +/- 11.7% for the controls and 14.3% +/- 7.8% for the cases (P < 0.05). The controls had a significan tly higher p53 response ratio and fewer chromatid breaks than the cases. We also found that a p53 increasing ratio was strongly related to cell cycle G(2) delay (gamma = 0.413; P = 0.002) and chromatid breaks (gamma = 0.384; P = 0.028). Therefore, we concluded that gamma -radiation-induced G(2) dela y, apoptosis, p53 increasing ratio, and chromatid breaks might potentially be used as susceptibility markers for lung cancer risk. A large epidemiolog y study is in progress to confirm these findings.