Over-expression of APAF-1 and caspase-9 augments radiation-induced apoptosis in U-373MG glioma cells

The p53 tumor-suppressor gene plays a critical role in radiation-induced apoptosis, Several genes, including Box and For, are involved in p53-mediated apoptosis, and their overexpression enhances the degree of radiation-induced apoptosis. Apaf-1 and caspase-9 have been reported to be downstream components of p53-mediated apoptosis, suggesting that these genes play a role in radiation-induced apoptosis, In this study, we transduced U-373MG cells harboring mutant p53 with the Apaf-1 and/or caspase-9 genes via adenoviral (Adv) vectors concomitant with X-ray irradiation and evaluated the degree of apoptosis, The percentage of apoptotic cells in U-373MG cells co-infected with the Adv for Apaf-1 (Adv-APAF-1) and that for caspase-9 (Adv-Casp9) and treated with irradiation (24%) was much higher than that in cells ca-infected with Adv-APAF-1 and Adv-Casp9 and not treated with irradiation (0.86%) and that in cells infected with either Adv-APAF-1 or Adv-Casp9 and treated with irradiation (2.0% or 2.6%, respectively). The apoptosis induced by co-transduction of Apaf-1 and caspase-9 and irradiation was repressed in cells that were co-infected with the Adv for Bcl-X-L but not in cells co-infected with the Adv for Bcl-2, These results indicate that Apaf-1 and caspase-9 play a role in radiation-induced apoptosis in cancer cells harboring mutant p53. Bcl-X-L may be critically involved in the radioresistance of cancer cells by repressing Apaf-1- and caspase-9-mediated apoptosis, Expression of Apaf-1 and caspase-9 in tumors may be an important determinant of the therapeutic effect of irradiation in cancer treatment. (C) 2001 Wiley-Liss, Inc.