The in vivo role of the Mdm2-MdmX interaction in p53 regulation

描述（申请人提供）：TP53是一种关键的肿瘤抑制基因，能够诱导细胞周期停滞、衰老和凋亡。典型地，TP53蛋白产物p53的主要负调节因子Mdm2被认为通过两种机制调节p53： 1) 通过直接结合 p53 反式激活结构域，抑制 p53 活性，2) 通过作为能够泛素化 p53 的 E3 泛素连接酶，将其靶向核输出和降解。除了同源蛋白 Mdm2 之外，MdmX 也在 p53 调节中发挥作用，主要通过与 Mdm2 类似的机制结合并阻断 p53 反式激活结构域。 Mdm2 和 MdmX 敲除小鼠均具有胚胎致死性，并通过同时删除 p53 来完全获救，这表明它们在 p53 调节中发挥着关键作用。 Mdm2C462A 敲入小鼠模型的开发可维持 Mdm2-p53 结合，但破坏 Mdm2 E3 连接酶活性，被发现会导致胚胎致死，并可通过同时删除 p53 来挽救。令人惊讶的是，这项研究表明，仅 Mdm2-p53 结合不足以调节 p53，并表明 Mdm2 RING Finger 结构域在 p53 调节中至关重要。除了破坏 Mdm2 E3 泛素活性外，该突变还会破坏 Mdm2-MdmX 异二聚化。由于 Mdm2C462A 突变破坏了环指结构域、E3 泛素连接酶活性和 MdmX 结合的功能，因此无法推断出这些变化中的哪一个导致了观察到的 p53 的错误调节。尽管进行了大量研究，但关于 Mdm2 和 MdmX 在体内如何调节 p53 的功能仍然未知。在体外，这种结合已被证明可以增强或挽救 Mdm2 E3 连接酶对 p53 的活性，但其在体内的作用尚不清楚。最近开发的 Mdm2Y487A 敲入小鼠保持了与 MdmX 和 p53 结合的能力，但破坏了 E3 泛素连接酶活性，从而可以分离这两个 Mdm2 RING 指结构域功能。通过利用该模型，我们希望进一步阐明 Mdm2 RING Finger 结构域在 p53 调节中的作用，因为进一步了解 p53 调节对于开发有效的治疗方法至关重要。

DESCRIPTION (provided by applicant): TP53 is a critical tumor suppressor gene capable of inducing cell cycle arrest, senescence, and apoptosis. Canonically, the primary negative regulator of the TP53 protein product p53, Mdm2, is considered to regulate p53 through two mechanisms; 1) through direct binding to the p53 transactivation domain, suppressing p53 activity, and 2) through functioning as an E3 ubiquitin ligase capable of ubiquitinating p53, targeting it for nuclear export and degradation. In addition to Mdm2, a homologous protein, MdmX also functions in p53 regulation, primarily through binding and blocking the p53 transactivation domain in a similar mechanism to Mdm2. Both Mdm2 and MdmX knockout mice are embryonically lethal, and rescued completely with concomitant deletion of p53, indicative of their critical role in p53 regulation. The development of an Mdm2C462A knock-in mouse model that maintains Mdm2-p53 binding, but disrupts Mdm2 E3 ligase activity, was found to result in embryonic lethality, rescued with simultaneous deletion of p53. Surprisingly, this study suggests that Mdm2-p53 binding alone is not sufficient for p53 regulation, and implicates the Mdm2 RING finger domain as critical in p53 regulation. Along with disrupting Mdm2 E3 ubiquitin activity, the mutation also disrupts Mdm2-MdmX heterodimerization. Because the Mdm2C462A mutation disrupts both functions of the RING finger domain, the E3 ubiquitin ligase activity and the MdmX binding, it cannot be deduced which of these changes is causing the observed misregulation of p53. Despite intensive study, much remains unknown about how Mdm2 and MdmX function in vivo to regulate p53. In vitro this binding has been demonstrated to amplify or rescue Mdm2 E3 ligase activity towards p53, but its role in vivo is not yet clear. Recent development of an Mdm2Y487A knock-in mouse, which maintains the ability to bind to MdmX and p53, but has disrupted E3 ubiquitin ligase activity has allowed for the separation of these two Mdm2 RING finger domain functions. Through utilizing this model, we hope to further elucidate the function of the Mdm2 RING finger domain in p53 regulation, as further understanding p53 regulation is critical in the development of effective therapeutics.