Tani E, Kitagawa H, Ikemoto H, Matsumoto T
Molecular Research Laboratory, Department of Neurosurgery, Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya, 663-8501, Hyogo, Japan.
FEBS Lett. 2001 Aug 24;504(1-2):53-8. doi: 10.1016/s0014-5793(01)02770-3.
Proteasome inhibitors were shown previously to induce mitochondria-independent and caspase-3-dependent apoptosis in human glioma cell lines by unknown mechanisms. Here, we showed that treatment with proteasome inhibitors, lactacystin or acetyl-leucinyl-leucinyl-norleucinal, led to elevation of the steady-state c-Myc protein but not c-myc mRNA, suggesting the accumulation of c-Myc protein by proteasome inhibitors. In addition, the marked association of c-Myc protein with ubiquitin by treatment with proteasome inhibitors indicated the involvement of proteasome in c-Myc proteolysis and the stabilization of c-Myc protein by proteasome inhibitors in vivo. The expression of Fas (also termed CD95 or APO-1) mRNA, if analyzed by reverse transcriptase polymerase chain reaction assay, was found to occur constitutively, and increased slightly by the treatment with proteasome inhibitors. In contrast, the expression of Fas ligand (FasL) mRNA was markedly induced temporarily before the activation of caspase-3 by the treatment. Agonistic anti-Fas antibody (CH11) induced apoptotic cell death, suggesting the presence of a functional Fas receptor. In addition, proteasome inhibitor-induced apoptosis was prevented by the addition of antagonistic anti-FasL antibody (4A5) or z-IETD.fmk, a potent inhibitor of caspase-8, indicating the involvement of the Fas receptor-ligand apoptotic signaling system in proteasome inhibitor-mediated apoptosis. Thus, it is suggested that proteasome inhibitors cause the accumulation of c-Myc protein which induces transiently FasL message to stimulate the Fas receptor-ligand apoptotic signaling pathway.
蛋白酶体抑制剂先前已被证明可通过未知机制在人胶质瘤细胞系中诱导不依赖线粒体且依赖半胱天冬酶 - 3的凋亡。在此，我们表明用蛋白酶体抑制剂、乳胞素或乙酰 - 亮氨酰 - 亮氨酰 - 正亮氨酸处理会导致稳态c - Myc蛋白水平升高，但c - myc mRNA水平未升高，这表明蛋白酶体抑制剂导致了c - Myc蛋白的积累。此外，用蛋白酶体抑制剂处理后c - Myc蛋白与泛素的显著结合表明蛋白酶体参与了c - Myc的蛋白水解，且蛋白酶体抑制剂在体内使c - Myc蛋白稳定。如果通过逆转录聚合酶链反应分析，发现Fas（也称为CD95或APO - 1）mRNA的表达是组成性的，并且用蛋白酶体抑制剂处理后略有增加。相比之下，Fas配体（FasL）mRNA的表达在处理激活半胱天冬酶 - 3之前会被显著短暂诱导。激动性抗Fas抗体（CH11）诱导凋亡细胞死亡，表明存在功能性Fas受体。此外，添加拮抗性抗FasL抗体（4A5）或z - IETD.fmk（一种有效的半胱天冬酶 - 8抑制剂）可阻止蛋白酶体抑制剂诱导的凋亡，这表明Fas受体 - 配体凋亡信号系统参与了蛋白酶体抑制剂介导的凋亡。因此，提示蛋白酶体抑制剂导致c - Myc蛋白积累，c - Myc蛋白会短暂诱导FasL信息以刺激Fas受体 - 配体凋亡信号通路。
