SHIFT OF THE CELLULAR OXIDATION-REDUCTION POTENTIAL IN NEURAL CELLS EXPRESSING BCL-2

Expression of the protooncogene bcl-2 inhibits both apoptotic and in s ome cases necrotic cell death in many cell types, including neural cel ls, and in response to a wide variety of inducers, The mechanism by wh ich the Bcl-2 protein acts to prevent cell death remains elusive. One mechanism by which Bcl-2 has been proposed to act is by decreasing the net cellular generation of reactive oxygen species. To evaluate this proposal, we measured activities of antioxidant enzymes as well as lev els of glutathione and pyridine nucleotides in control and bcl-2 trans fectants in two different neural cell lines-rat pheochromocytoma PC12 and the hypothalamic GnRH cell line GT1-7, Both neural cell lines over expressing bcl-2 had elevated total glutathione levels when compared w ith control transfectants. The ratios of oxidized glutathione to total glutathione in PC12 and GT1-7 cells overexpressing bcl-2 were signifi cantly reduced, In addition, the NAD(+)/NADH ratio of bcl-2-expressing PC12 and GT1-7 cells was two- to threefold less than that of control cell lines. GT1-7 cells overexpressing bcl-2 had the same level of glu tathione peroxidase, catalase, superoxide dismutase, and glutathione r eductase activities as control cells, PC12 cells overexpressing bcl-2 had a twofold increase in superoxide dismutase and catalase activity w hen compared with matched control transfected cells, The levels of glu tathione peroxidase and glutathione reductase in PC12 cells overexpres sing bcl-2 were similar to those of control cells, These results indic ate that the overexpression of bcl-2 shifts the cellular redox potenti al to a more reduced state, without consistently affecting the major c ellular antioxidant enzymes.