Sequential Cleavage of Poly(ADP‐Ribose)polymerase and Appearance of a Small Bax‐Immunoreactive Protein Are Blocked by Bcl‐XL and Caspase Inhibitors During Staurosporine‐Induced Dopaminergic Neuronal Apoptosis

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Abstract
To assess the role of Bcl-XL and its splice derivative, Bcl-Xs, in staurosporine-induced cell death, we used a dopaminergic cell line, MN9D, transfected with bcl-xL (MN9D/Bcl-XL), bcl-xs (MN9D/Bcl-Xs), or control vector (MN9D/Neo). Only 8.6% of MN9D/Neo cells survived after 24 h of 1 μM staurosporine treatment. Caspase activity was implicated because a caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-fmk), attenuated staurosporine-induced cell death. Bcl-XL rescued MN9D cells from death (89.4% viable cells), whereas Bcl-Xs had little or no effect. Bcl-XL prevented morphologically apoptotic changes as well as cleavage of poly(ADP-ribose)polymerase (PARP) induced by staurosporine. It is interesting that a small Bax-immunoreactive protein appeared 4-8 h after PARP cleavage in MN9D/Neo cells. The appearance of the small Bax-immunoreactive protein, however, may be cell type-specific as it was not observed in PC12 cells after staurosporine treatment. The sequential cleavage of PARP and the appearance of the small Bax-immunoreactive protein in MN9D cells were blocked either by Z-VAD-fmk or by Bcl-XL. Thus, our present study suggests that Bcl-XL but not Bcl-Xs prevents staurosporine-induced apoptosis by inhibiting the caspase activation that may be directly or indirectly responsible for the appearance of the small Bax-immunoreactive protein in some types of neurons.