p53蛋白精氨酸脱氨化及其功能调节研究

P53 protein is an important transcription factor in cell growth, DNA damage, and apoptosis. Posttranslational modifications ofp53 include phosphorylation, acetylation, methylation, and ubiquitination, which can regulate the stability and transcriptional activity of p53. Deamination or citrullination, catalyzed by a family of calcium-binding enzymes, the peptidyl arginine deaminases (PADI) proteins, is a non-protein amino acid which is present in many cellular proteins. As the only one of PADI family member localized in nuclear, PADI4 participates in the process of tumorigenesis. Recruitment of PADI4 to p53 target gene promoter by p53 resulted in histones deaminating and reduction of the chromatin accessibility. However, whether PADI4 is directly modified P53 and deaminating can regulate the function of p53 have not been reported. We found early, PADI4 deaminated p53 directly in vitro and in vivo. The deaminating p53 obviously repressed its acetylation at K382, to reduce the recruitment of p53 on the target gene promoters. In addition, PADI4 also leads to the G1/S phase cell cycle arrest and inhibit the cell growth in p53-dependent manner. Deaminating-mimic mutants from arginine to glutamine displayed lower transcriptional activity, and promoted the cell cycle arrest. Therefore, the application of quasi aims to research the molecular mechanisms of new modification of p53-deamination, to explore the regulatory pathways of deaminated p53, which will provide new targets for therapeutic method of p53 related tumors.

p53蛋白作为一个重要的转录因子在细胞生长、DNA损伤及细胞凋亡等过程中起重要作用。p53的翻译后修饰包括磷酸化、乙酰化、泛素化、甲基化等，可以调节其稳定性和转录活性。脱氨化或瓜氨酸化是一种由肽酰精氨酸脱亚胺酶（peptidyl arginine deiminase，PADI）所催化的蛋白质精氨酸翻译后修饰。PADI4和p53关联研究备受关注。已有报道PADI4被p53募集到靶基因的启动子区，催化组蛋白发生脱氨从而降低染色质的可接近性，抑制基因表达。但是，PADI4是否直接修饰p53以及脱氨化是否可以调节p53的功能则未见报道。我们前期发现，PADI4能够直接修饰p53，并且，脱氨化p53可以影响其转录活性。因此，本申请拟深入研究p53新的修饰类型-脱氨化修饰的分子机制，探讨脱氨化p53的调节途径，为阐明PADI4-p53通路的机制提供新的思路，为p53相关肿瘤治疗方法提供新的靶点。

瓜氨酸是由一系列钙结合酶(PADI)催化的一种非蛋白编码氨基酸，存在于许多细胞蛋白中。 PADI4作为定位于核内的唯一PADI家族成员，参与肿瘤发生过程。虽然PADI4被招募到抑癌基因p53的靶基因启动子，导致组蛋白瓜氨酸化和染色质可达性的降低然而，但是，瓜氨酸化修饰的生理功能仍然不明确。我们发现p53通过PADI4催化发生瓜氨酸化修饰。在p53调控域内单个精氨酸残基（Arg）的瓜氨酸化明显抑制其转录活性，并且促进肿瘤发生。只有在很低的水平上才能将瓜氨酸化修饰的p53可以被招募到靶基因调控区；瓜氨酸化修饰p53的乙酰化程度降低。 我们的结果揭示了一种新型的p53翻译后修饰以及瓜氨酸化和乙酰化之间的相互作用，阐明了PADI4调控p53的新机制。 这一发现支持了PADI4作为癌症潜在治疗生物标志物的研究。