A post-ubiquitination role for MDM2 and hHR23A in the p53 degradation pathway
A post-ubiquitination role for MDM2 and hHR23A in the p53 degradation pathway
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DOI：
10.1038/sj.onc.1207540
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发表时间：
2004-05-20
期刊：
影响因子：
8
通讯作者：
Grossman, SR
中科院分区：
文献类型：
--
作者：
Brignone, C;Bradley, KE;Grossman, SR
消除泛素/蛋白酶体依赖性p53的周转对其激活至关重要。UbL-UBA蛋白，包括Rad23 （hHR23）的人类同源蛋白，可能调节蛋白酶体对底物（如p53）的降解，因为它们能够与泛素化底物和蛋白酶体相互作用。在人类细胞系中，sirna介导的hHR23A或hHR23B的缺失加速了p53的降解。相反，hHR23蛋白的过表达导致p53泛素化的积累，纯化的hHR23蛋白也阻断了p53蛋白酶体的体外降解。鉴定出hHR23-MDM2复合物，提示MDM2和hHR23共同调控p53蛋白酶体降解。与这一假设相一致的是，在体内与hHR23A结合增加的MDM2突变体能够泛素化，但不能降解p53。此外，通过敲低hHR23A的siRNA，该MDM2突变体的缺陷表型得以恢复。我们的数据表明，MDM2在泛素化后p53降解途径的一个步骤中起作用，抵消hHR23对p53转换的抑制。此外，我们的数据表明，泛素连接酶/UbL-UBA蛋白复合物，如MDM2/hHR23复合物，可能在调节蛋白酶体降解底物方面发挥普遍作用。
Abrogation of ubiquitin/proteasome-dependent turnover of p53 is critical for its activation. UbL-UBA proteins, including human homolog of Rad23 (hHR23) proteins, may regulate proteasomal degradation of substrates such as p53, due to their ability to interact with both ubiquitinated substrates and the proteasome. siRNA-mediated depletion of hHR23A or hHR23B in human cell lines accelerated p53 degradation. In contrast, overexpression of hHR23 proteins led to the accumulation of ubiquitinated p53, and purified hHR23 proteins also blocked p53 proteasome degradation in vitro. An hHR23-MDM2 complex was identified, suggesting that MDM2 and hHR23 cooperate in the regulation of p53 proteasome degradation. Consistent with this hypothesis, an MDM2 mutant that demonstrated increased binding in vivo to hHR23A was able to ubiquitinate, but not degrade p53. Moreover, the defective phenotype of this MDM2 mutant was rescued by siRNA knockdown of hHR23A. Our data indicate that MDM2 acts at a step in the p53 degradation pathway after ubiquitination, to counteract hHR23 inhibition of p53 turnover. Moreover, our data suggest the possibility that ubiquitin ligase/UbL-UBA protein complexes, as exemplified by the MDM2/hHR23 complex, may serve a general role in regulating substrate degradation by the proteasome.