依托泊苷通过线粒体信号通路释放细胞色素C诱导Jurkat白血病细胞凋亡

目的：研究在人类Jurkat白血病细胞株中依托泊苷诱导凋亡的分子机制，揭示由依托泊苷启动的凋亡信号通路。 方法：分别用annexin V-FITC和碘化丙啶（PI）染色，通过流式细胞仪测定annexin V阳性和出现亚二倍体DNA的凋亡细胞。以3,3＇-dihexyloxyacarbocyanine iodide ［DiOC6(3)］为染色剂，采用流式细胞术检测细胞线粒体膜电位的变化。采用离心技术分离细胞的胞浆与线粒体。细胞色素c从线粒体转入胞浆，caspase-3的激活，多聚二磷酸腺苷核糖聚合酶（PARP）的切割等蛋白质的表达由免疫印迹技术（Western blotting）检测。 结果：依托泊苷诱导Jurkat白血病细胞凋亡，细胞凋亡与依托泊苷的作用时间呈线性关系。广谱的caspase抑制剂zVAD.fmk可抑制依托泊苷诱导的DNA片段化和磷脂酰丝氨酸外翻。依托泊苷引起的线粒体膜电位下降早于DNA片段化和磷脂酰丝氨酸外翻，形成明显对照的是zVAD.fmk不能阻断依托泊苷诱导的线粒体膜电位的下降。依托泊苷介导细胞色素c从线粒体释放到胞浆，激活caspase-3，caspase-3的底物PARP被切割。 结论：依托泊苷诱导Jurkat白血病细胞株凋亡的机制是降低线粒体膜电位和释放细胞色素c到细胞浆启动线粒体信号转导通路, 最终激活caspase而导致细胞凋亡。

Etoposide induces apoptosis via mitochondrial signaling pathway with cytochrome c release in Jurkat leukemia cells

AIM: To investigate the molecular mechanisms of apoptosis and to elucidate the apoptosis signaling pathway triggered by etoposide in Jurkat human leukemia cells. METHODS: Apoptosis was detected using annexin V - FITC and propidium iodide (PI) staining, respectively, and annexin V - FITC positive cells and hypodiploid cells were analyzed by flow cytometry. Mitochondrial membrane potential (△Ψm) was detected using 3,3' - dihexyloxycarbocyanine iodide DiOC6 (3)] staining and △Ψm low cells were analyzed by flow cytometry. Preparation of cytosolic extracts and isolation of mitochondria were completed by centrifugation. Western blotting analysis was used to evaluate the level of cytochrome c, caspase - 3, and poly ( ADP - ribose) polymerase (PARP) expression. RESULTS: Etoposide induced apoptosis showing phosphatidylserine externalization and DNA fragmentation in a time - dependent manner and the apoptosis could be inhibited by a broad caspase inhibitor benzyloxycarbonyl - Val - Ala - Asp - fluoromethylketone ( zVAD. fmk). Collapse of △Ψm induced by etoposide preceded DNA fragmentation and phosphatidylserine externalization. In contrast, it was not blocked by zVAD. fmk. Etoposide caused cytochrome c release from mitochondria into cytosol, subsequent activation of caspase-3 (32 kD) presented with an intermediate (20 kD) and its active product (17kD), and cleavage of full- length PARP (116 kD) into the so- called apoptotic 85 kD fragment. CONCLUSION:Etoposide - induced Jurkat cell apoptosis is initiated through mitochondria signaling pathway with cytochrome c release into cytoplasm and caspase is the ultimate executioner of cell apoptosis.