MDM2 and MDMX function together as the p53 E3 ligase

描述（由申请人提供）：作为细胞应激反应的主要调节因子，p53在细胞命运决定中起重要作用。因此，必须精确地调节p53的活性。在参与p53控制的众多蛋白质中，MDM 2和MDMX是关键参与者，如小鼠中敲除mdm 2或mdmx导致p53依赖性致死性的事实所证明的。然而，很少有人知道为什么MDM 2和MDMX都需要在p53的控制，MDM 2和MDMX介导的p53调控的分子机制仍然没有完全确定。其他人和我们已经表明，MDM 2和MDMX形成了一种异源复合物，更重要的是，它们在p53调控中相互依赖。结构和生物化学证据进一步表明MDM 2/MDMX杂复合物的形成是有利的。我们的假设是，异源复合物代表了MDM 2和MDMX在p53控制下的生理形式。拟议的研究将使用小鼠模型直接测试这一假设。我们还将充分表征MDM 2/MDMX杂合物在p53泛素化和调节p53对应激的反应。具体目标是：1）使用动物模型检查MDM 2/MDMX复合物在p53调节中的作用; 2）表征MDM 2/MDMX复合物介导的p53泛素化; 3）研究调节MDM 2/MDMX复合物的细胞机制。随着基因敲入小鼠的成功产生，我们非常有利地进行了拟议的研究。从拟议的工作中获得的发现不仅有望阐明MDM 2和MDMX的非冗余功能，而且还将提供一种新的p53调控机制。 公共卫生相关性：本申请旨在通过使用动物模型直接测试MDM 2/MDMX异源复合物在p53控制中的重要性。同时，MDM 2/MDMX复合物介导的p53泛素化将被充分表征，并将研究MDM 2/MDMX调节的细胞机制。通过这些调查，我们将测试的假设，MDM 2/MDMX异源复合物是生理E3连接酶的p53，这，如果被证明，不仅代表了一个新的范式p53的调节，但也揭示了非冗余功能的MDM 2和MDMX。此外，MDM 2/MDMX复合物在p53控制中的关键作用为p53激活提供了理想的靶点，例如异源复合物的解离，这可能具有治疗意义。

DESCRIPTION (provided by applicant): As a master regulator of cellular stress response, p53 plays an important role in cell fate decisions. The activity of p53 therefore must be precisely regulated. Among numerous proteins involved in p53 control, MDM2 and MDMX are the key players, as evidenced by the fact that knockout of either mdm2 or mdmx in mice resulted in p53-dependent lethality. However, little is known about why both MDM2 and MDMX are required in p53 control, and the molecular mechanisms underlying MDM2 and MDMX-mediated p53 regulation remain not fully defined. Others and we have shown that MDM2 and MDMX form a heterocomplex and, more importantly, that they depend on each other in p53 regulation. Structural and biochemical evidence further indicate that formation of the MDM2/MDMX heterocomplex is favored. Our hypothesis is that the heterocomplex represents the physiological form of MDM2 and MDMX in p53 control. The proposed studies will use mouse models to directly test this hypothesis. We will also fully characterize the MDM2/MDMX heterocomplex in p53 ubiquitination and in regulation of the p53 response to stress. The specific aims are: 1) using animal models to examine a role of the MDM2/MDMX complex in p53 regulation; 2) characterize the MDM2/MDMX complex-mediated p53 ubiquitination; 3) investigate cellular mechanisms that regulate the MDM2/MDMX complex. With the knock-in mice being successfully generated, we are very favorably positioned to carry out the proposed studies. The findings obtained from the proposed work are expected not only to shed light on the non-redundant function of MDM2 and MDMX, but also to provide a novel mechanism of p53 regulation. PUBLIC HEALTH RELEVANCE: This application aims to directly test the importance of the MDM2/MDMX heterocomplex in p53 control by using animal models. In parallel, the MDM2/MDMX complex-mediated p53 ubiquitination will be fully characterized and cellular mechanisms of MDM2/MDMX regulation will be investigated. Through these lines of investigation, we will test the hypothesis that the MDM2/MDMX heterocomplex is the physiological E3 ligase for p53, which, if proven, will not only represent a new paradigm of p53 regulation but also shed lights on the non-redundant function of MDM2 and MDMX. In addition, the pivotal role of the MDM2/MDMX complex in p53 control presents an ideal target for p53 activation, e.g. disassociation of the heterocomplex, which may have therapeutic implications.