Hua Guoqiang, Zhang Qixiang, Fan Zusen
National Laboratory of Biomacromolecules and Center for Infection and Immunity, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
J Biol Chem. 2007 Jul 13;282(28):20553-60. doi: 10.1074/jbc.M703196200. Epub 2007 May 18.
Natural killer (NK) cells play an important role in innate immunity against virally infected or transformed cells as the first defense line. Granzyme M (GzmM) is an orphan granzyme that is constitutively highly expressed in NK cells and is consistent with NK cell-mediated cytolysis. We recently demonstrated that GzmM induces caspase-dependent apoptosis with DNA fragmentation through direct cleavage of inhibitor of caspase-activated DNase (ICAD). However, the molecular mechanisms for GzmM-induced apoptosis are unclear. We found GzmM causes mitochondrial swelling and loss of mitochondrial transmembrane potential. Moreover, GzmM initiates reactive oxygen species (ROS) generation and cytochrome c release. Heat shock protein 75 (HSP75, also known as TRAP1) acts as an antagonist of ROS and protects cells from GzmM-mediated apoptosis. GzmM cleaves TRAP1 and abolishes its antagonistic function to ROS, resulting in ROS accumulation. Silencing TRAP1 through RNA interference increases ROS accumulation, whereas TRAP1 overexpression attenuates ROS production. ROS accumulation is in accordance with the release of cytochrome c from mitochondria and enhances GzmM-mediated apoptosis.
自然杀伤（NK）细胞作为第一道防线，在针对病毒感染或转化细胞的固有免疫中发挥着重要作用。颗粒酶M（GzmM）是一种孤儿颗粒酶，在NK细胞中组成性高表达，且与NK细胞介导的细胞溶解作用一致。我们最近证明，GzmM通过直接切割半胱天冬酶激活的脱氧核糖核酸酶（ICAD）抑制剂，诱导依赖半胱天冬酶的凋亡并伴有DNA片段化。然而，GzmM诱导凋亡的分子机制尚不清楚。我们发现GzmM会导致线粒体肿胀和线粒体跨膜电位丧失。此外，GzmM会引发活性氧（ROS）生成和细胞色素c释放。热休克蛋白75（HSP75，也称为TRAP1）作为ROS的拮抗剂，保护细胞免受GzmM介导的凋亡。GzmM切割TRAP1并消除其对ROS的拮抗功能，导致ROS积累。通过RNA干扰使TRAP1沉默会增加ROS积累，而TRAP1过表达则会减弱ROS产生。ROS积累与细胞色素c从线粒体的释放一致，并增强GzmM介导的凋亡。
