Brentnall Matthew, Rodriguez-Menocal Luis, De Guevara Rebeka Ladron, Cepero Enrique, Boise Lawrence H
Departments of Hematology and Medical Oncology and Cell Biology, Winship Cancer Institute of Emory University, 1365 Clifton Road NE Bldg:C, Rm:4012, Atlanta, GA 30322, USA.
BMC Cell Biol. 2013 Jul 9;14:32. doi: 10.1186/1471-2121-14-32.
Apoptosis is a form of programmed cell death that is regulated by the Bcl-2 family and caspase family of proteins. The caspase cascade responsible for executing cell death following cytochrome c release is well described; however the distinct roles of caspases-9, -3 and -7 during this process are not completely defined.
Here we demonstrate several unique functions for each of these caspases during cell death. Specific inhibition of caspase-9 allows for efficient release of cytochrome c, but blocks changes in mitochondrial morphology and ROS production. We show that caspase-9 can cleave Bid into tBid at amino acid 59 and that this cleavage of Bid is required for ROS production following serum withdrawal. We also demonstrate that caspase-3-deficient MEFs are less sensitive to intrinsic cell death stimulation, yet have higher ROS production. In contrast, caspase-7-deficient MEFs are not resistance to intrinsic cell death, but remain attached to the ECM.
Taken together, these data suggest that caspase-9 is required for mitochondrial morphological changes and ROS production by cleaving and activating Bid into tBid. After activation by caspase-9, caspase-3 inhibits ROS production and is required for efficient execution of apoptosis, while effector caspase-7 is required for apoptotic cell detachment.
细胞凋亡是一种程序性细胞死亡形式，受Bcl-2家族和半胱天冬酶家族蛋白调控。细胞色素c释放后负责执行细胞死亡的半胱天冬酶级联反应已得到充分描述；然而，在此过程中半胱天冬酶-9、-3和-7的不同作用尚未完全明确。
在此，我们展示了这些半胱天冬酶在细胞死亡过程中的几种独特功能。对半胱天冬酶-9的特异性抑制可使细胞色素c有效释放，但会阻断线粒体形态变化和活性氧生成。我们发现半胱天冬酶-9可在第59位氨基酸处将Bid切割成tBid，血清撤出后活性氧生成需要Bid的这种切割。我们还证明，半胱天冬酶-3缺陷的小鼠胚胎成纤维细胞（MEFs）对内在细胞死亡刺激的敏感性较低，但活性氧生成较高。相比之下，半胱天冬酶-7缺陷的MEFs对内在细胞死亡不具有抗性，但仍附着于细胞外基质（ECM）。
综上所述，这些数据表明半胱天冬酶-9通过将Bid切割并激活为tBid，参与线粒体形态变化和活性氧生成。经半胱天冬酶-9激活后，半胱天冬酶-3抑制活性氧生成，是有效执行细胞凋亡所必需的，而效应半胱天冬酶-7则是凋亡细胞脱离所必需的。
