The pro-death role of autophagy and apoptosis in cell death induced by the BH3 mimetic gossypol

Gossypol has been identified as a natural BH3 mimetic and a small-molecule inhibitor of Bcl-2 that can induce apoptosis in various cancer cell lines. In this study, we evaluated the effect of gossypol on apoptosis-proficient (wild-type [WT] mouse embryonic fibroblasts, MEFs) and apoptosis-deficient cells (Bax -/- /Bak -/- MEFs) in order to determine whether apoptosis indeed plays an essential death-promoting role in gossypol-mediated cell death. Unexpectedly, we found that Bax -/- /Bak -/- double-knockout (DKO) MEFs were more sensitive than the WT cells to gossypol-induced cell death. Gossypol caused progressive emergence of both apoptotic and necrotic cells in DKO MEFs; this result suggests that gossypol induces Bax/Bak-independent apoptosis. Conversely, fluorescence-activated cell sorting profiles showed no apoptotic cell death in WT MEFs. Rather, incubation of WT MEFs with gossypol markedly induced autophagy, as evidenced by punctate patterns of LC3 immunoreactivity, indicative of apoptosis-independent autophagic cell death. Nonetheless, there was only limited induction of autophagy in DKO MEFs. No significant differences between WT and DKO MEFs were observed in cell cycle profiles. Gossypol caused a weak increase of the percentage of cells at the G 2 /M checkpoint in the two cell lines, with a concomitant small decrease in the number of cells in the S phase. Taken together, our results suggest that apoptotic cell death is induced by gossypol in DKO MEFs, whereas autophagy plays a death-promoting role in gossypol-mediated death of WT MEFs cells.