Read Stuart H, Baliga Belinda C, Ekert Paul G, Vaux David L, Kumar Sharad
Hanson Institute, Adelaide, Australia 5000.
J Cell Biol. 2002 Dec 9;159(5):739-45. doi: 10.1083/jcb.200209004. Epub 2002 Dec 2.
Caspase activation is a key event in apoptosis execution. In stress-induced apoptosis, the mitochondrial pathway of caspase activation is believed to be of central importance. In this pathway, cytochrome c released from mitochondria facilitates the formation of an Apaf-1 apoptosome that recruits and activates caspase-9. Recent data indicate that in some cells caspase-9 may not be the initiator caspase in stress-mediated apoptosis because caspase-2 is required upstream of mitochondria for the release of cytochrome c and other apoptogenic factors. To determine how caspase-2 is activated, we have studied the formation of a complex that mediates caspase-2 activation. Using gel filtration analysis of cell lysates, we show that caspase-2 is spontaneously recruited to a large protein complex independent of cytochrome c and Apaf-1 and that recruitment of caspase-2 to this complex is sufficient to mediate its activation. Using substrate-binding assays, we also provide the first evidence that caspase-2 activation may occur without processing of the precursor molecule. Our data are consistent with a model where caspase-2 activation occurs by oligomerization, independent of the Apaf-1 apoptosome.
半胱天冬酶激活是细胞凋亡执行过程中的关键事件。在应激诱导的细胞凋亡中，半胱天冬酶激活的线粒体途径被认为至关重要。在该途径中，从线粒体释放的细胞色素c促进Apaf-1凋亡小体的形成，后者招募并激活半胱天冬酶-9。最近的数据表明，在某些细胞中，半胱天冬酶-9可能不是应激介导的细胞凋亡中的起始半胱天冬酶，因为在细胞色素c和其他凋亡因子从线粒体释放之前，需要半胱天冬酶-2。为了确定半胱天冬酶-2是如何被激活的，我们研究了介导半胱天冬酶-2激活的复合物的形成。通过对细胞裂解物进行凝胶过滤分析，我们发现半胱天冬酶-2会自发地募集到一个与细胞色素c和Apaf-1无关的大型蛋白质复合物中，并且半胱天冬酶-2募集到该复合物足以介导其激活。通过底物结合试验，我们还首次证明半胱天冬酶-2的激活可能在没有前体分子加工的情况下发生。我们的数据与一个模型一致，即半胱天冬酶-2通过寡聚化激活，与Apaf-1凋亡小体无关。
