Effect of exogenous wild-type p53 on melanoma cell death pathways induced by irradiation at different linear energy transfer.

We investigated the effect of exogenous wild-type p53 on the radiation-induced cells apoptosis and necrosis at different levels of linear energy transfer (LET) to evaluate its mechanisms. The human melanoma cell line A375, which bears wild-type p53 gene status, was used, as well as the transfectant A375 cells (A375/p53) with adenoviral vector containing the wild-type p53 gene. We exposed these cells to X-rays and to accelerated carbon-ion (C-) beams. Cellular sensitivities were determined by using clonogenic assay. Apoptotic and necrotic cell deaths were determined morphologically by dual staining (acridine orange and ethidium bromide) using fluorescence microscopy. We discovered that (1) there was no significant difference in survival fraction between A375 cells and A375/p53 cells irradiated by C-beams with greater than 32 KeV/microm LET, (2) although apoptosis in the two kinds of cells increased in an LET-dependent manner, exogenous wild-type P53 induced cell apoptosis efficiently in A375/p53 relative to A375 cells with X-rays or high-LET irradiation, and (3) by high-LET irradiation, the number of necrosis in A375 cells increased significantly (P < 0.05) in comparison with A375/p53 cells. These results indicate that in high-LET irradiation apoptosis induction is p53 dependent partly and exogenous wild-type P53 plays an important role in modulating cell death type, although there was no significant difference in cellular radiosensitivities. Our observation in the study offers the potential application of high-LET radiation combined with p53 in the management of human patients with melanoma.