Henis-Korenblit Sivan, Shani Gidi, Sines Tal, Marash Lea, Shohat Galit, Kimchi Adi
Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
Proc Natl Acad Sci U S A. 2002 Apr 16;99(8):5400-5. doi: 10.1073/pnas.082102499. Epub 2002 Apr 9.
Apoptosis is characterized by a translation switch from cap-dependent to internal ribosome entry site (IRES)-mediated protein translation. During apoptosis, several members of the eukaryotic initiation factor (eIF)4G family are cleaved specifically by caspases. Here we investigated which of the caspase-cleaved eIF4G family members could support cap-independent translation through IRES elements that retain activity in the dying cell. We focused on two major fragments arising from the cleavage of eIF4GI and death-associated protein 5 (DAP5) proteins (eIF4GI M-FAG/p76 and DAP5/p86, respectively), because they are the only potential candidates to preserve the minimal scaffold function needed to mediate translation. Transfection-based experiments in cell cultures indicated that expression of DAP5/p86 in cells stimulated protein translation from the IRESs of c-Myc, Apaf-1, DAP5, and XIAP. In contrast, these IRESs were refractory to the ectopically expressed eIF4GI M-FAG/p76. Furthermore, our study provides in vivo evidence that the caspase-mediated removal of the C-terminal tail of DAP5/p97 relieves an inhibitory effect on the protein's ability to support cap-independent translation through the DAP5 IRES. Altogether, the data suggest that DAP5 is a caspase-activated translation factor that mediates translation through a repertoire of IRES elements, supporting the translation of apoptosis-related proteins.
细胞凋亡的特征是翻译从帽依赖性转变为内部核糖体进入位点（IRES）介导的蛋白质翻译。在细胞凋亡过程中，真核起始因子（eIF）4G家族的几个成员被半胱天冬酶特异性切割。在这里，我们研究了哪些被半胱天冬酶切割的eIF4G家族成员可以通过在垂死细胞中保持活性的IRES元件来支持不依赖帽的翻译。我们聚焦于eIF4GI和死亡相关蛋白5（DAP5）蛋白切割产生的两个主要片段（分别为eIF4GI M-FAG/p76和DAP5/p86），因为它们是保留介导翻译所需最小支架功能的唯一潜在候选者。基于细胞培养的转染实验表明，细胞中DAP5/p86的表达刺激了来自c-Myc、Apaf-1、DAP5和XIAP的IRES的蛋白质翻译。相比之下，这些IRES对异位表达的eIF4GI M-FAG/p76不敏感。此外，我们的研究提供了体内证据，即半胱天冬酶介导的DAP5/p97 C末端尾巴的去除减轻了对该蛋白通过DAP5 IRES支持不依赖帽翻译能力的抑制作用。总之，数据表明DAP5是一种半胱天冬酶激活的翻译因子，它通过一系列IRES元件介导翻译，支持凋亡相关蛋白的翻译。
