Hyperthermia induces translocation of apoptosis-inducing factor (AIF) and apoptosis in human glioma cell lines

In the hyperthermal treatment, the wild type (wt) p53 plays an important role in apoptosis induction in the tumor cells. In human gliomas, p53 frequently has some form of mutation. The mutant type (mt) p53 does not work properly as a tumor suppressor and this may result in poor responses during treatment. We investigated the relationship between apoptosis-inducing factor (AIF) and apoptosis under various thermal conditions (43, 45, and 47degreesC for 1 h) using four p53-wild or -mutant human glioma cell lines (A172, T98G, U251MG, and YKG-1). AIF translocation from the mitochondria to the nucleus under hyperthermal conditions was demonstrated by confocal laser microscopy. The percentage of AIF-positive nuclei increased significantly in comparison with the control in all cell lines and in all temperature groups except for YKG-1 at 47degreesC. Immunoblot analyses of the nuclear fraction of each cell line revealed temperature-dependent increases in AIF. A simultaneous release of cytochrome c from the mitochondria to the cytosol was noted. A flow cytometric analysis showed that apoptosis induction occurred more often in a temperature-dependent manner in the 45 and 47degreesC groups than in the control group. These findings indicate that the hyperthermal conditions can lead to AIF translocation and apoptotic cell death in the p53-mutant human glioma cells. The present report is the first description of AIF-induced apoptosis in hyperthermia.