Caspase-6 is the direct activator of caspase-8 in the cytochrome c-induced apoptosis pathway:: Absolute requirement for removal of caspase-6 prodomain
Caspase-6 is the direct activator of caspase-8 in the cytochrome c-induced apoptosis pathway:: Absolute requirement for removal of caspase-6 prodomain
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DOI：
10.1038/sj.cdd.4401065
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发表时间：
2002-10-01
影响因子：
12.4
通讯作者：
Downward, J
中科院分区：
文献类型：
--
作者：
Cowling, V;Downward, J
由线粒体释放细胞色素c引起的半胱天冬酶活化是由一系列因素引发的细胞凋亡机制的重要组成部分。在该途径中，通过半胱天冬酶-8激活Bid促进细胞色素c的进一步释放，从而完成半胱天冬酶激活的正反馈回路。虽然在该途径中激活胱天蛋白酶-8所必需的胱天蛋白酶的身份是已知的，但仍不清楚哪种蛋白酶直接切割胱天蛋白酶-8。为了确定负责的因素，我们进行了生化纯化的caspase-8裂解活性的细胞溶质提取物，细胞色素c已被添加。在这里，我们报告，caspase-6是唯一的细胞色素c激活的Jurkat细胞提取物中的可溶性蛋白酶，具有显着的caspase-8裂解活性。此外，我们纯化的半胱天冬酶-6足以诱导细胞提取物中的Bid依赖性细胞色素c释放活性。抑制细胞中的半胱天冬酶-6活性显著抑制半胱天冬酶-8切割和凋亡，因此确立半胱天冬酶-6作为体内半胱天冬酶-8的主要激活剂，并证实该途径在促进凋亡中具有关键作用。我们还表明，caspase-6是无活性的，直到短的前结构域被删除。我们认为，需要两个不同的裂解步骤激活效应caspase可能代表了一个有效的机制，限制自发caspase激活和异常进入凋亡。
Caspase activation resulting from cytochrome c release from the mitochondria is an essential component of the mechanism of apoptosis initiated by a range of factors. The activation of Bid by caspase-8 in this pathway promotes further cytochrome c release, thereby completing a positive feedback loop of caspase activation. Although the identity of the caspases necessary for caspase-8 activation in this pathway are known, it is still unclear which protease directly cleaves caspase-8. In order to identify the factor responsible we undertook a biochemical purification of caspase-8 cleaving activity in cytosolic extracts to which cytochrome c had been added. Here we report that caspase-6 is the only soluble protease in cytochrome c activated Jurkat cell extracts that has significant caspase-8 cleaving activity. Furthermore the caspase-6 that we purified was sufficient to induce Bid dependent cytochrome c releasing activity in cell extracts. Inhibition of caspase-6 activity in cells significantly inhibited caspase-8 cleavage and apoptosis, therefore establishing caspase-6 as a major activator of caspase-8 in vivo and confirming that this pathway can have a critical role in promotion of apoptosis. We also show that caspase-6 is inactive until the short prodomain is removed. We suggest that the requirement for two distinct cleavage steps to activate an effector caspase may represent an effective mechanism for restriction of spontaneous caspase activation and aberrant entry into apoptosis.