Involvement of interleukin-1 beta-converting enzyme in apoptosis of irradiated retinoblastomas

PURPOSE. TO investigate whether interleukin-1 beta-converting enzyme (ICE), a mammalian homologue of the Caenorhabditis elegans cell death gene ced-3, is involved in gamma-irradiation-induced apoptosis (programmed cell death) of human retinoblastoma cells. METHODS. The induction of apoptotic cell death in human retinoblastoma cell lines WERI-Rb-1 and Y79 by gamma-irradiation was determined with a modifie d 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide colorimetri c assay and the DNA-binding fluorochrome bis (benzimide) trihydro-chloride (Hoechst 33258) staining. The change of ICE protein level in tumor cells du ring apoptosis was determined by immunoblotting assay. Whether the spe cifi c tetrapeptide ICE inhibitor Ac-YVAD-CMK affected gamma-irradiation-induced apoptosis in tumor cells was also examined. The effect of ICE overexpressi on on tumor cells was evaluated by a transient transfection assay using ICE expression vector. RESULTS. gamma-Irradiation inhibited the cell viability of WERI-Rb-1 and Y7 9 cells in a dose-dependent manner and induced apoptosis. The protein level of ICE was remarkably enhanced after the treatment. The apoptotic cell dea th induced by gamma-irradiation was suppressed by the tetrapeptide ICE inhi bitor Ac-YVAD-CMK. Moreover, overexpression of ICE induced apoptosis in tum or cells. CONCLUSIONS. These findings suggest that ICE may play an important role in gamma-irradiation-induced apoptosis in retinoblastoma cells. Transfer of th e ICE gene induces apoptosis in these cells without gamma-irradiation.