SM-20 is a novel mitochondrial protein that causes caspase-dependent cell death in nerve growth factor-dependent neurons
SM-20 is a novel mitochondrial protein that causes caspase-dependent cell death in nerve growth factor-dependent neurons
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DOI：
10.1074/jbc.m008407200
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发表时间：
2001-02-16
影响因子：
4.8
通讯作者：
Freemann, RS
中科院分区：
文献类型：
--
作者：
Lipscomb, EA;Sarmiere, PD;Freemann, RS
当缺乏神经生长因子(NGF)时，交感神经元发生蛋白质合成依赖性的细胞凋亡。在NGF剥夺的交感神经元中，SM-20的表达上调，在NGF存在的情况下，异位SM-20足以促进神经元的死亡。我们现在报告SM-20是一种线粒体蛋白，通过caspase依赖的机制促进细胞死亡。SM-20免疫荧光呈点状分布于细胞质中，与细胞色素氧化酶I和线粒体选择性染料共定位。对SM-20/二氢叶酸还原酶融合蛋白的分析表明，SM-20的前25个氨基酸含有一个功能性的线粒体靶向序列。SM-20的氨基末端截短形式并不局限于线粒体，而是定位于整个细胞质和细胞核。然而，截短的SM-20保留了诱导神经元死亡的能力，与野生型蛋白相似，SM-20诱导的死亡伴随着caspase-3的激活，并被一般的caspase抑制剂阻断。此外，在一般caspase抑制剂阻断细胞死亡的条件下，SM-20的过度表达并没有导致细胞色素c从线粒体中广泛释放，这些结果表明SM-20是一种新的线粒体蛋白，可能是神经营养素撤退介导的细胞死亡的重要中介。
Sympathetic neurons undergo protein synthesis-dependent apoptosis when deprived of nerve growth factor (NGF). Expression of SM-20 is up-regulated in NGF-deprived sympathetic neurons, and ectopic SM-20 is sufficient to promote neuronal death in the presence of NGF. We now report that SM-20 is a mitochondrial protein that promotes cell death through a caspase-dependent mechanism. SM-20 immunofluorescenee was present in the cytoplasm in a punctate pattern that colocalized with cytochrome oxidase I and with mitochondria-selective dyes. Analysis of SM-20/dihydrofolate reductase fusion proteins revealed that the first 25 amino acids of SM-20 contain a functional mitochondrial targeting sequence. An amino-terminal truncated form of SM-20 was not restricted to mitochondria but instead localized throughout the cytosol and nucleus. Nevertheless, the truncated SM-20 retained the ability to induce neuronal death, similar to the wild type protein, SM-20-induced death was accompanied by caspase-3 activation and was blocked by a general caspase inhibitor. Additionally, overexpression of SM-20, under conditions where cell death is blocked by a general caspase inhibitor, did not result in widespread release of cytochrome c from mitochondria, These results indicate that SM-20 is a novel mitochondrial protein that may be an important mediator of neurotrophin-withdrawal-mediated cell death.