Voehringer D W, McConkey D J, McDonnell T J, Brisbay S, Meyn R E
Department of Experimental Radiation Oncology, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Proc Natl Acad Sci U S A. 1998 Mar 17;95(6):2956-60. doi: 10.1073/pnas.95.6.2956.
In this study we used HeLa cells transfected with a conditional Bcl-2 expression construct to study the effects of Bcl-2 on reduced glutathione (GSH) metabolism. Our previous work demonstrated that depletion of GSH by culturing cells in tissue culture medium lacking the amino acids cysteine and methionine, essential for GSH biosynthesis, caused cells overexpressing Bcl-2 to become sensitized to apoptotic induction. Here we report that Bcl-2 also dramatically alters GSH compartmentalization. Cellular distribution of GSH, assayed by confocal microscopy, revealed that when Bcl-2 expression was suppressed GSH was uniformly distributed primarily in the cytosol, whereas overexpression of Bcl-2 led to a relocalization of GSH into the nucleus. Isolated nuclei readily accumulated radiolabeled GSH and maintained higher nuclear GSH concentration in direct relation to Bcl-2 nuclear protein levels. Moreover, exogenous GSH blocked apoptotic changes and caspase activity in isolated nuclei exposed to the pro-apoptotic protease granzyme B. Our results indicate that one of the functions of Bcl-2 is to promote sequestration of GSH into the nucleus, thereby altering nuclear redox and blocking caspase activity as well as other nuclear alterations characteristic of apoptosis. We speculate that this mechanism contributes to the suppression of apoptosis in cells with elevated Bcl-2 levels.
在本研究中，我们使用转染了条件性Bcl-2表达构建体的HeLa细胞来研究Bcl-2对还原型谷胱甘肽（GSH）代谢的影响。我们之前的工作表明，通过在缺乏GSH生物合成所必需的氨基酸半胱氨酸和蛋氨酸的组织培养基中培养细胞来消耗GSH，会使过表达Bcl-2的细胞对凋亡诱导变得敏感。在此我们报告，Bcl-2还会显著改变GSH的区室化。通过共聚焦显微镜检测GSH的细胞分布，结果显示，当Bcl-2表达被抑制时，GSH主要均匀分布于胞质溶胶中，而Bcl-2的过表达则导致GSH重新定位到细胞核中。分离的细胞核很容易积累放射性标记的GSH，并维持较高的核GSH浓度，且与Bcl-2核蛋白水平直接相关。此外，外源性GSH可阻断暴露于促凋亡蛋白酶颗粒酶B的分离细胞核中的凋亡变化和半胱天冬酶活性。我们的结果表明，Bcl-2的功能之一是促进GSH隔离到细胞核中，从而改变核氧化还原状态，阻断半胱天冬酶活性以及凋亡特有的其他核变化。我们推测，这种机制有助于抑制Bcl-2水平升高的细胞中的凋亡。
