Institute of Molecular Medicine and Cell Research, Center for Biochemistry and Molecular Cell Research, Albert Ludwigs University Freiburg, Freiburg, Germany.
Cell Death Differ. 2010 Jul;17(7):1167-78. doi: 10.1038/cdd.2009.214. Epub 2010 Jan 22.
Apoptotic stimuli have been shown to trigger lysosomal membrane permeability (LMP), leading to the release of cathepsins, which activate death signaling pathways in the cytosol. However, it is unknown whether this process is an initiating or amplifying event in apoptosis. In this study, we used fibroblasts and monocytes exposed to etoposide, ultraviolet light, FasL or deprived of interleukin-3 (IL-3) to show that LMP and the cytosolic release of cathepsins B, L and D consistently depends on Bax/Bak and components of the apoptosome. Neither Bax nor Bak resided on the lysosomes, indicating that lysosomes were not directly perforated by Bax/Bak but by effectors downstream of the apoptosome. Detailed kinetic analysis of cells lacking cathepsin B or L or treated with the cysteine protease inhibitor, E64d, revealed a delay in these cells in etoposide- and IL-3 deprivation-induced caspase-3 activation and apoptosis induction but not clonogenic survival, indicating that cathepsins amplify rather than initiate apoptosis.
凋亡刺激已被证明会触发溶酶体膜通透性（LMP），导致组织蛋白酶的释放，从而激活细胞质中的死亡信号通路。然而，尚不清楚这一过程是凋亡的起始事件还是放大事件。在这项研究中，我们使用暴露于依托泊苷、紫外线、FasL 或缺乏白细胞介素-3（IL-3）的成纤维细胞和单核细胞，表明 LMP 和组织蛋白酶 B、L 和 D 的细胞质释放始终依赖于 Bax/Bak 和凋亡体的成分。Bax 和 Bak 都不在溶酶体上，这表明溶酶体不是被 Bax/Bak 直接穿孔，而是被凋亡体下游的效应物穿孔。对缺乏组织蛋白酶 B 或 L 的细胞或用半胱氨酸蛋白酶抑制剂 E64d 处理的细胞进行详细的动力学分析，揭示了这些细胞在依托泊苷和 IL-3 剥夺诱导的 caspase-3 激活和凋亡诱导中存在延迟，但集落形成存活不受影响，表明组织蛋白酶放大而不是起始凋亡。
