Tolerance of high levels of wild-type p53 in transformed epithelial cells dependent on auto-regulation by mdm-2
Tolerance of high levels of wild-type p53 in transformed epithelial cells dependent on auto-regulation by mdm-2
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DOI：
10.1038/sj.onc.1201018
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发表时间：
1997-04-17
期刊：
影响因子：
8
通讯作者：
WynfordThomas, D
中科院分区：
文献类型：
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作者：
Blaydes, JP;Gire, V;WynfordThomas, D
相当比例的人类癌症在基因中没有潜在突变的情况下表达高水平的p53蛋白。使用转化（Vh 1）和非转化（FRTL-5）大鼠甲状腺上皮细胞系作为模型，我们已经研究了高水平的野生型p53的耐受机制。用p53依赖性报告构建体稳定转染表明，Vh 1细胞中“过量”野生型p53与p53依赖性转录的可比增加无关（尽管对紫外线照射的反应被保留）。Mdm-2结合p53并抑制其反式激活活性，在不存在基因扩增的情况下以p53依赖性方式在Vh 1细胞中过表达。此外，通过显微注射针对mdm-2的p53结合结构域的抗体来破坏Vh 1细胞中p53-mdm-2复合物的形成导致p53依赖性转录的急剧增加。由于Vh 1细胞中只有一小部分p53与mdm-2复合（大多数未结合的蛋白质处于潜伏形式），这表明mdm-2选择性地结合p53库，否则p53将作为序列特异性转录激活因子而具有活性。我们认为，在某些类型的肿瘤中，p53驱动的mdm-2反馈回路的“敏感性”可能足以阻止游离的、活性的p53达到生长停滞或凋亡所需的水平，使其成为旨在破坏p53-mdm-2相互作用的治疗的理想靶点。
A significant proportion of human cancers express high levels of p53 protein in the absence of an underlying mutation in the gene. Using transformed (Vh1) and non-transformed (FRTL-5) rat thyroid epithelial cell lines as a model, we have examined the mechanisms by which high levels of wild-type p53 may be tolerated. Stable transfection with p53-dependent reporter constructs demonstrated that the 'excess' wild-type p53 in Vh1 cells is not associated with a comparable increase in p53-dependent transcription (though the response to u.v. irradiation is retained). Mdm-2, which binds p53 and inhibits its transactivation activity, is overexpressed in Vh1 cells in the absence of gene amplification and in a p53-dependent manner. Furthermore disruption of p53-mdm-2 complex formation in Vh1 cells by microinjection of an antibody to the p53-binding domain of mdm-2 resulted in a dramatic increase in p53-dependent transcription. Since only a small proportion of the p53 in Vh1 cells was found to be in complex with mdm-2 (the majority of unbound protein being in a latent form), this suggests that mdm-2 selectively binds a pool of p53 that would otherwise be active as a sequence-specific activator of transcription. We suggest that, in some types of tumour, the 'sensitivity' of the p53-driven mdm-2 feedback loop may be sufficient to prevent free, active p53 reaching the level required for growth arrest or apoptosis, making them an ideal target for therapies designed to disrupt p53-mdm-2 interactions.