Tepper C G, Seldin M F
Rowe Program in Genetics, Departments of Biological Chemistry and Medicine, UC Davis School of Medicine, Davis, CA 95616, USA.
Blood. 1999 Sep 1;94(5):1727-37.
Ligation of the Fas receptor induces death-inducing signaling complex (DISC) formation, caspase activation, and subsequent apoptotic death of several cell types. Epstein-Barr virus (EBV)-positive group III Burkitt's lymphoma (BL) cell lines have a marked resistance to Fas-mediated apoptosis, although expressing each of the DISC components, Fas/ APO-1-associated death domain protein (FADD), and caspase-8 (FLICE/MACH/Mch5). The apoptotic pathway distal to the DISC is intact because ceramide analogs, staurosporine, and granzyme B activate caspase-3 and induce apoptosis. Fas resistance was not explained by the putative death-attenuating caspase-8 isoforms. However, while Fas-activated cytosolic extracts from sensitive cells were capable of processing both procaspase-8 and procaspase-3 into active subunit forms, resistant cell extracts did not possess either of these activities. Accordingly, reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed higher transcript levels for the FLICE-inhibitory protein (FLIP(L)) in resistant cells and the ratio of caspase-8 to FLIP(L) measured by competition RT-PCR analysis directly correlated with susceptibility to Fas-mediated apoptosis of all cell lines. In addition, modification of the caspase-8/FLIP(L) ratio by caspase-8 or FLIP(L) overexpression was able to alter the susceptibility status of the cell lines tested. Our results imply that the relative levels of caspase-8 and FLIP(L) are an important determinant of susceptibility to Fas-mediated apoptosis.
Fas受体的结扎诱导死亡诱导信号复合物（DISC）形成、半胱天冬酶激活以及随后几种细胞类型的凋亡死亡。爱泼斯坦-巴尔病毒（EBV）阳性的III型伯基特淋巴瘤（BL）细胞系对Fas介导的凋亡具有显著抗性，尽管它们表达DISC的各个组分，即Fas/APO-1相关死亡结构域蛋白（FADD）和半胱天冬酶-8（FLICE/MACH/Mch5）。由于神经酰胺类似物、星形孢菌素和颗粒酶B可激活半胱天冬酶-3并诱导凋亡，因此DISC远端的凋亡途径是完整的。Fas抗性不能用假定的死亡减弱型半胱天冬酶-8同工型来解释。然而，虽然来自敏感细胞的Fas激活的胞质提取物能够将无活性的半胱天冬酶-8和无活性的半胱天冬酶-3加工成活性亚基形式，但抗性细胞提取物不具备这两种活性。因此，逆转录聚合酶链反应（RT-PCR）分析显示抗性细胞中FLICE抑制蛋白（FLIP(L)）的转录水平较高，并且通过竞争RT-PCR分析测定的半胱天冬酶-8与FLIP(L)的比率与所有细胞系对Fas介导的凋亡的敏感性直接相关。此外，通过过表达半胱天冬酶-8或FLIP(L)来改变半胱天冬酶-8/FLIP(L)比率能够改变所测试细胞系的敏感性状态。我们的结果表明，半胱天冬酶-8和FLIP(L)的相对水平是对Fas介导的凋亡敏感性的重要决定因素。
