Two different mechanisms of apoptosis resistance observed in interferon-β induced apoptosis of human glioma cells

Interferon (IFN)-beta is known to exert cytostatic or cytocidal effects in human glioma cells and is widely used in the treatment for gliomas. However, precise mechanisms of cell death induced by IFN-beta are not well understood. In this study, the authors investigated the intracellular signal transduction of IFN-beta in human glioma cells. The cell death process observed in susceptible cells SK-MG-1 was accompanied by characteristic morphological changes of apoptosis, processing of caspases, and DNA fragmentation. Use of caspase inhibitors confirmed the activation of caspases, however activated executioner caspase was caspase-7 rather than caspases-3 or -6. Activation of DNA endonuclease, DNase-gamma was also observed. Observation of other IFN-beta relatively resistant glioma cells (U251SP, T98G, U251MG, U87MG, SK-AO2) revealed two different mechanisms of apoptosis resistance. In contrast to T98G, U87MG, and SK-AO2 which showed no activation of caspases, surprisingly, all the apoptosis process except DNase-gamma activation was observed in U251SP and U251MG cells. Collectively, these findings indicate that IFN-beta induced apoptosis in human glioma cells through activation of caspase-7 and activation of DNase-gamma. The similar activations of caspases were found also in some of the apoptosis resistant cells. These findings may help to improve the IFN-beta therapy in near future.