Caspase-9 transduction overrides the resistance mechanism against p53-mediated apoptosis in U-87MG glioma cells.

Abstract

Conflicting reports have been published with regard to the relationship between the efficacy of p53 gene therapy and the p53 status of gliomas. In this study, we evaluated whether U-87MG glioma cells harboring wild-type p53 and U251 and U-373MG glioma cells harboring mutated p53 demonstrate different sensitivities to p53-induced apoptosis. In addition, we tested whether transduction of Bax or caspase-9, which are downstream components of p53-induced apoptosis, can override the resistance mechanism of U-87MG cells to apoptosis. We transduced U-87MG, U251, and U-373MG glioma cells with p53, Bax, or caspase-9 genes via adenovirus (Adv) vectors, to induce the same level of respective proteins, and evaluated the degree of apoptosis. U-87MG cells were highly resistant to Adv for p53 (Adv-p53)-mediated apoptosis, whereas U251 and U-373 cells underwent extensive apoptosis after Adv-p53 infection. In U-87MG cells, the elevation of Bax and Fas was not as marked as that observed in U251 and U-373MG cells after Adv-p53 infection. Endogenous expression of Bcl-XL and Bcl-2 in U-87MG cells was greater than that in U251 and U-373MG cells. U-87MG cells were more resistant to Bax-mediated apoptosis than were U251 or U-373MG cells. In contrast, U-87MG cells were more sensitive to caspase-9-mediated apoptosis than were U251 or U-373MG cells, suggesting that transduction of caspase-9 may override the resistance mechanism of U-87MG to p53-mediated apoptosis. These results demonstrate that proapoptotic function induced by p53 transduction in U-87MG cells was repressed at several steps and that induction of caspase-9 may circumvent this resistance mechanism.