Hsp105alpha enhances stress-induced apoptosis but not necrosis in mouse embryonal f9 cells

Hsp105alpha, which belongs to the HSP105/110 family, is expressed at especially high levels in the brain in mammals and has been shown to prevent stress-induced apoptosis in neuronal cells. This protein is also expressed transiently at high levels during mouse embryogenesis, and is characteristically found in apoptotic cells and bodies in embryos. In the present study, to elucidate a role of Hsp105alpha in embryonal cells, we established Hsp105alpha-overexpressing F9 cells, and examined the effect of Hsp105alpha on cell death induced by etoposide, heat shock or cycloheximide. Apoptotic cell death was induced in cells treated with etoposide or heat shock, and necrotic cell death was induced in cells by cycloheximide. The apoptosis was enhanced by overexpression of HSP105alpha, whereas the necrosis was not affected by overexpression of HSP105alpha. Furthermore, Hsp105alpha seemed to modulate the stress-induced apoptosis at different steps of the apoptotic process depending on the stress stimuli. The present findings together with the previous observation on neuronal cells suggested that Hsp105 has opposite effects on stress-induced apoptosis depending on the cell type; a pro-apoptotic effect in embryonal cells and an anti-apoptotic effect in neuronal cells. The apoptosis-enhancing activity of Hsp105alpha may play an important role during embryogenesis.