鼻咽癌中P53复合体的结构与功能研究

The tumor suppressor gene p53 is essential for the prevention of cancer development. More than half of human cancers have been found to carry p53 mutations. However, p53 expression is widely up-regulated in nasopharyngeal carcinoma (NPC) while its mutation is rarely found, which suggests that p53 might be inactivated in nasopharyngeal carcinoma by some unknown mechanism. P53 binds its cognate sequences and regulates the expression of a variety of downstream genes involved in cell cycle arrest, DNA repair and apoptosis. In our previous studies, we have solved the first crystal structure of a self-assembled p53 core domain tetramer bound to a physiological site which is shown to be high-affinity, and identified 14-3-3σ as a critical partner of p53 using proteomic methods. In the proposed studies, we plan to extend these studies to p53 binding low-affinity pro-apoptotic sites, which contain two decameric sites with a spacer of 1-13 bps. We also plan to include 14-3-3σ to study the crystal structure of p53/14-3-3σ complex. We expect to make a series of major breakthroughs on the structure and function studies of p53 in the next several years that may help illustrate the mechanism of p53 dysfunction in NPC.

p53抑癌基因在肿瘤发生发展过程中发挥重要作用，50%以上的肿瘤有p53突变。在鼻咽癌中p53突变十分罕见， 但绝大多数鼻咽癌有p53表达显著上调，提示p53在鼻咽癌中失去抑瘤活性，具体机制并不清楚。p53通过形成一个大型的蛋白质-核酸复合体，调节细胞周期、DNA修复及凋亡，发挥细胞生理功能和肿瘤抑制功能。在前期工作中，我们已解析了p53与DNA高亲和力位点结合的复合体结构，并且采用蛋白质组学方法在鼻咽癌中发现了14-3-3σ与P53相互作用。在此基础上，我们将进一步解析p53与低亲和力的促凋亡基因位点结合的复合体结构，探讨P53与两段非连续的DNA"半结合位点"结合的机制。我们还将解析p53与14-3-3σ结合的复合体结构，探寻14-3-3σ参与P53复合体的形成机制。这些研究有助于阐明鼻咽癌中p53功能异常的分子机制，为进一步提高鼻咽癌的防治水平提供新的理论依据。

鼻咽癌（nasopharyngeal carcinoma，NPC）是我国南方及东南亚常见的一种恶性肿瘤，具有高的侵袭和转移恶性。60-80%以上的NPC组织和几乎100%的NPC细胞株有p53蛋白过表达。本课题主要采用蛋白晶体学方法研究P53核心结构域与低亲和力调控位点结合的大型复合体的高分辨率晶体结构，以及结合于DNA位点的p53和14-3-3σ复合体的高分辨晶体结构。本研究首次解析了P53核心结构域与含有单碱基间隔的BAX-RE复合物的晶体结构，揭示了p53与含有一个碱基对的非连续性“半结合位点”的结合机制，为阐明p53是如何调控此类促凋亡基因的表达提供了有力的理论基础，同时为以p53蛋白复合物等结构为基础进行的抗癌药物设计及提高鼻咽癌的防治水平提供了新的理论依据。

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