BAX ACCELERATES STAUROSPORINE-INDUCED BUT SUPPRESSES NIGERICIN-INDUCED NEURONAL CELL-DEATH

BAX, a member of the Bcl-2 multigene family, is known to promote apopt osis. To investigate the role of Bax in an experimentally induced cell death of the murine dopaminergic neuronal cell line (MN9D), we establ ished MN9D cells stably over-expressing murine Bar (MN9D/Bar) or vecto r alone (MN9D/Neo). In MN9D/Neo cells treated with either 1 mu M staur osporine or 0.1 mu M nigericin, a ladder pattern of DNA fragmentation was induced. As expected, over-expression of Bar in MN9D cells acceler ated staurosporine-induced cell death as measured by the MTT reduction assay (62.3% survival in MN9D/Neo us 27.0% survival in MN9D/Bax). Sur prizingly, both nigericin-induced cell death and its accompanying DNA fragmentation were largely attenuated in MN9D/Bax cells (22.0% surviva l in MN9D/Neo us 86.7% survival in MN9D/Bax). Similar patterns were ob served in two other MN9D/Bax cell lines. Cleavage of poly(ADP-ribose)p olymerase caused by nigericin was greatly attenuated in MN9D/Bax cells suggesting that, like Bcl-2, Bax suppresses nigericin-induced cell de ath by inhibiting the activation of cysteine proteases. Thus, our data imply that Bar acts as a negative or positive regulator of cell death depending on the type of death stimulus applied to the cell.