Bcl-x(L) overexpression inhibits taxol-induced Yama protease activity and apoptosis

Intracellularly, the anticancer drug taxol induces tubulin polymerization and mitotic arrest, followed by apoptosis. The DNA repair enzyme poly(ADP-ribose) polymerase (PARP) and lamins are known to be degraded during apoptosis. PARP is a substrate for the Yama protease, which is encoded by the CPP32β/Yama gene, whereas lamins are degraded by the Yama and lamin proteases. In the present studies, we determined the effects of enforced overexpression of the antiapoptosis Bcl-x(L) protein on taxol-mediated microtubule and cell cycle perturbations, as well as on taxol-induced apoptosis and associated Yama protease activity in human myeloid leukemia HL- 60 cells. Our data demonstrate that high Bcl-x(L) levels do not affect the microtubular bundling or mitotic arrest due to taxol but significantly inhibit the morphological, flow cytometric, and DNA fragmentation features associated with taxol-induced apoptosis. This resulted in a significant improvement in the survival of taxol-treated cells that possess high Bcl- x(L) levels. In the control HL-60 cells, following taxol treatment, whereas the mRNA of Yama was not induced, taxol-induced apoptosis was associated with Yama activation and PARP as well as lamin B1 degradation. These features were blocked by coculture of these cells with the cysteine protease inhibitor YVAD-cmk as well as in cells with overexpression of Bcl-x(L). These results suggest that Bcl-x(L) antagonizes taxol-induced apoptosis by a mechanism that interferes with the activation of a key protease involved in the execution of apoptosis.