Kangas A, Nicholson D W, Hölttä E
Haartman Institute, Department of Pathology, University of Helsinki, Finland.
Oncogene. 1998 Jan 22;16(3):387-98. doi: 10.1038/sj.onc.1201779.
c-Myc is a transcriptional activator implicated in the control of cell proliferation, differentiation and transformation, but is also involved in the regulation of programmed cell death, apoptosis. Despite intensive research, the molecular mechanisms by which c-Myc triggers and executes cell death remain still elusive. Here, we made use of Rat 1A MycER cells expressing a conditionally active c-Myc protein and tested first the hypothesis that ornithine decarboxylase (ODC), which is a transcriptional target of c-Myc, were a mediator of c-Myc-induced apoptosis. However, our results show that the activity of ODC is not required for the c-Myc-mediated apoptosis to occur in these cells. We also found that the expression of p53, p21waf1/cip1, Bcl-2, Bax, Bcl-xL, Bad and cyclins D1, E, A and B did not show any significant changes following c-Myc induction. But, our studies revealed that the c-Myc induced apoptosis is associated with a specific cleavage of poly(ADPribose) polymerase (PARP), suggesting that a cysteine protease of the ICE/CED-3 family is involved. Moreover, we found that the cysteine protease CPP32/Caspase-3, which is known to cleave PARP, is processed from its inactive form to an active protease composed of 17 and 12 kDa subunits; whilst Ich-1/Caspase-2 belonging to another subset of this protease family was not processed/ activated following c-Myc activation. The activation of CPP32 and apoptotic cell death were inhibited by addition of Z-VAD-fmk, a universal inhibitor of ICE-like proteases. Further, a selective inhibitor of CPP32-like proteases (Z-DEVD-fmk) partly inhibited apoptosis. These results provide evidence that the ICE/CED3-family proteases, CPP32 and likely others, play a critical role in the execution of a nuclear proto-oncogene, c-Myc-induced apoptosis.
c-Myc是一种转录激活因子，与细胞增殖、分化和转化的调控有关，但也参与程序性细胞死亡（即凋亡）的调节。尽管进行了深入研究，c-Myc触发并执行细胞死亡的分子机制仍然难以捉摸。在此，我们利用表达条件性活性c-Myc蛋白的大鼠1A MycER细胞，首先测试了鸟氨酸脱羧酶（ODC）作为c-Myc的转录靶点是c-Myc诱导凋亡的介导因子这一假设。然而，我们的结果表明，在这些细胞中，c-Myc介导的凋亡发生并不需要ODC的活性。我们还发现，在c-Myc诱导后，p53、p21waf1/cip1、Bcl-2、Bax、Bcl-xL、Bad以及细胞周期蛋白D1、E、A和B的表达均未显示出任何显著变化。但是，我们的研究表明，c-Myc诱导的凋亡与聚（ADP-核糖）聚合酶（PARP）的特异性切割有关，这表明ICE/CED-3家族的一种半胱氨酸蛋白酶参与其中。此外，我们发现已知可切割PARP的半胱氨酸蛋白酶CPP32/Caspase-3从其无活性形式加工成由17 kDa和12 kDa亚基组成的活性蛋白酶；而属于该蛋白酶家族另一个亚组的Ich-1/Caspase-2在c-Myc激活后未被加工/激活。添加ICE样蛋白酶的通用抑制剂Z-VAD-fmk可抑制CPP32的激活和凋亡性细胞死亡。此外，CPP32样蛋白酶的选择性抑制剂（Z-DEVD-fmk）部分抑制凋亡。这些结果证明，ICE/CED3家族蛋白酶、CPP32以及可能的其他蛋白酶在核原癌基因c-Myc诱导的凋亡执行中起关键作用。
