Suppression of the deubiquitinating enzyme USP5 causes the accumulation of unanchored polyubiquitin and the activation of p53.
Suppression of the deubiquitinating enzyme USP5 causes the accumulation of unanchored polyubiquitin and the activation of p53.
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DOI：
10.1074/jbc.m805871200
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发表时间：
2009-02-20
期刊：
影响因子：
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通讯作者：
Saville MK
中科院分区：
文献类型：
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作者：
Dayal S;Sparks A;Jacob J;Allende-Vega N;Lane DP;Saville MK
p53及其阻遏物Mdm 2都受到泛素化和蛋白酶体降解的影响。我们发现，敲低去泛素化酶USP 5（异肽酶T）导致p53的水平和转录活性增加。USP 5的抑制稳定了p53，而它对Mdm 2的稳定性几乎没有影响。这为p53的转录激活提供了机制。USP 5敲低干扰泛素化p53的降解，而不是减弱p53泛素化。体外研究表明，USP 5的优选底物是未锚定的聚泛素。与此一致，我们首次在哺乳动物系统中观察到，USP 5对Lys-48连接的聚泛素分解做出了重大贡献，并且USP 5的抑制导致未锚定的聚泛素链的积累。泛素的C-末端突变体（G75 A/G76 A）的异位表达（其也引起游离聚泛素的积累）概括了USP 5敲低对p53途径的影响。我们提出了一个模型，其中p53被选择性地稳定，因为在USP 5敲低后积累的未锚定的多聚泛素能够与泛素化的p53竞争，但不能与Mdm 2竞争蛋白酶体识别。这提出了蛋白酶体识别p53和Mdm 2存在显著差异的可能性。这些差异可以在治疗上加以利用。我们的研究揭示了一种新的p53调控机制，并确定USP 5作为p53激活治疗药物治疗癌症的潜在靶点。
Both p53 and its repressor Mdm2 are subject to ubiquitination and proteasomal degradation. We show that knockdown of the deubiquitinating enzyme USP5 (isopeptidase T) results in an increase in the level and transcriptional activity of p53. Suppression of USP5 stabilizes p53, whereas it has little or no effect on the stability of Mdm2. This provides a mechanism for transcriptional activation of p53. USP5 knockdown interferes with the degradation of ubiquitinated p53 rather than attenuating p53 ubiquitination. In vitro studies have shown that a preferred substrate for USP5 is unanchored polyubiquitin. Consistent with this, we observed for the first time in a mammalian system that USP5 makes a major contribution to Lys-48-linked polyubiquitin disassembly and that suppression of USP5 results in the accumulation of unanchored polyubiquitin chains. Ectopic expression of a C-terminal mutant of ubiquitin (G75A/G76A), which also causes the accumulation of free polyubiquitin, recapitulates the effects of USP5 knockdown on the p53 pathway. We propose a model in which p53 is selectively stabilized because the unanchored polyubiquitin that accumulates after USP5 knockdown is able to compete with ubiquitinated p53 but not with Mdm2 for proteasomal recognition. This raises the possibility that there are significant differences in proteasomal recognition of p53 and Mdm2. These differences could be exploited therapeutically. Our study reveals a novel mechanism for regulation of p53 and identifies USP5 as a potential target for p53 activating therapeutic agents for the treatment of cancer.