Overexpression of HA-Bax but not Bcl-2 or Bcl-XL attenuates 6-hydroxydopamine-induced neuronal apoptosis

Bax, a member of the Bcl-2 gene family, is known to promote apoptosis in many cases but to block cell death under certain conditions. To investigate the potential role of Bax in B-hydroxydopamine (6-OHDA)induced cell death, we first established and characterized a dopaminergic neuronal cell Line (MN9D) stably overexpressing hemagglutinin epitope-tagged Bax (MN9D/HA-Bax) as well as control clones (MN9D/Neo). Treatment of MN9D/Neo cells with 6-OHDA induced typical apoptotic cell death accompanied by shrinkage of the cell, nuclear condensation, and DNA fragmentation as demonstrated by light microscopy and agarose gel analysis. Overexpression of HA-Bax in MN9D cells was shown to attenuate 6-OHDA-induced cell death as determined by the MTT reduction assay and agarose gel analysis for DNAfragmentation. Western blot analysis revealed that cleavage of poly(ADP-ribose)polymerase induced by 6-OHDA was attenuated in MN9D/HA-Bax cells, In contrast, overexpression of a well-known cell death-inhibiting protein such as Bcl-2 or Bcl-X-L did not attenuate 6-OHDA-induced cell death. Interestingly, cell death induced by hydrogen peroxide (0.25-2.0 mM) was significantly accelerated, whereas the rate of cell death induced by menadione (10-50 mu M) was not affected in MN9D/HA-Bax cells. Thus, our present data suggest that the functionally diverse roles of Bax may be determined by the type of stress applied to the cell. (C) 1998 Academic Press.