Apoptosis induced by high-LET radiations is not affected by cellular p53 gene status

To learn more about the biological effects of high-linear energy transfer (LET) radiations, we examined radiation-induced apoptosis in response to high-LET radiations in cells with wild-type, mutated and null p53 gene. Three human lung cancer cell lines were used. These lines had identical genotypes, except for the p53 gene. Cells were exposed to X-rays or high-LET radiations (13 - 200 keV microm(-1)) using different nuclei ion beams. Cellular radiation sensitivities were determined with the use of colony-forming assays. Apoptosis was detected and quantified using Hoechst 33342 staining with fluorescence microscopy. It was found that (1) there was no significant difference in cellular sensitivity to high-LET radiation (>85 keV microm(-1)), although the sensitivity of wild-type p53 cells to X-rays was higher than that of mutated p53 or p53-null cells; (2) X-ray-induced apoptosis at higher frequencies in wild-type p53 cells when compared with mutated p53 and p53-null cells; and (3) Fe beams (200 keV microm(-1)) induced apoptosis in a p53-independent manner. The results indicate that high-LET radiations induces apoptosis in human lung cancer cells in a manner that does not seem to depend on the p53 gene status of the cells.