Ellerby L M, Ellerby H M, Park S M, Holleran A L, Murphy A N, Fiskum G, Kane D J, Testa M P, Kayalar C, Bredesen D E
Program on Aging, Burnham Institute, La Jolla Cancer Research Center, CA 92037, USA.
J Neurochem. 1996 Sep;67(3):1259-67. doi: 10.1046/j.1471-4159.1996.67031259.x.
Expression of the protooncogene bcl-2 inhibits both apoptotic and in some cases necrotic cell death in many cell types, including neural cells, and in response to a wide variety of inducers. The mechanism by which 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 levels of glutathione and pyridine nucleotides in control and bcl-2 transfectants in two different neural cell lines-rat pheochromocytoma PC12 and the hypothalamic GnRH cell line GT1-7. Both neural cell lines overexpressing bcl-2 had elevated total glutathione levels when compared with control transfectants. The ratios of oxidized glutathione to total glutathione in PC12 and GT1-7 cells overexpressing bcl-2 were significantly 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 glutathione peroxidase, catalase, superoxide dismutase, and glutathione reductase activities as control cells. PC12 cells overexpressing bcl-2 had a twofold increase in superoxide dismutase and catalase activity when compared with matched control transfected cells. The levels of glutathione peroxidase and glutathione reductase in PC12 cells overexpressing bcl-2 were similar to those of control cells. These results indicate that the overexpression of bcl-2 shifts the cellular redox potential to a more reduced state, without consistently affecting the major cellular antioxidant enzymes.
原癌基因bcl-2的表达在包括神经细胞在内的多种细胞类型中，以及在对多种诱导剂的反应中，均能抑制凋亡，在某些情况下还能抑制坏死性细胞死亡。Bcl-2蛋白预防细胞死亡的机制仍不清楚。有人提出Bcl-2发挥作用的一种机制是减少细胞内活性氧的净生成。为了评估这一观点，我们在两种不同的神经细胞系——大鼠嗜铬细胞瘤PC12和下丘脑促性腺激素释放激素细胞系GT1-7中，测量了对照转染细胞和bcl-2转染细胞中抗氧化酶的活性以及谷胱甘肽和吡啶核苷酸的水平。与对照转染细胞相比，两种过表达bcl-2的神经细胞系的总谷胱甘肽水平均有所升高。过表达bcl-2的PC12和GT1-7细胞中氧化型谷胱甘肽与总谷胱甘肽的比率显著降低。此外，表达bcl-2的PC12和GT1-7细胞的NAD+/NADH比率比对照细胞系低两到三倍。过表达bcl-2的GT1-7细胞与对照细胞具有相同水平的谷胱甘肽过氧化物酶、过氧化氢酶、超氧化物歧化酶和谷胱甘肽还原酶活性。与匹配的对照转染细胞相比，过表达bcl-2的PC12细胞的超氧化物歧化酶和过氧化氢酶活性增加了两倍。过表达bcl-2的PC12细胞中谷胱甘肽过氧化物酶和谷胱甘肽还原酶的水平与对照细胞相似。这些结果表明，bcl-2的过表达使细胞氧化还原电位转变为更还原的状态，而没有持续影响主要的细胞抗氧化酶。
