应激情况下mdm2调节WRN触发p53诱导的细胞衰老

The p53 tumor suppressor plays a critical role in inducing senescence. However, p53 can also induce cell growth arrest, apoptosis besides senescence. How cells choose to go cellular senescence after p53 activation is still not clear. Our preliminary studies found that besides p53, mdm2 can also specifically ubiquitinate WRN protein and significantly shorten its half-life. Mutations in the WRN protein, a caretaker of the genome, resulted in Werner syndrome, which is characterized by premature aging phenotypes and cancer predisposition. As an E3 ligase for both p53 and WRN, mdm2 could play a critical role in regulating p53 induced cellular senescence. Our preliminary studies found that besides p53, mdm2 can also specifically ubiquitinate WRN protein and significantly shorten its half-life. In this project, we will (1) Demonstrate mdm2 as E3 ligase of WRN by both in vitro and in vivo assays; (2) Investigate the regulation of WRN ubiquitination and degradation in cells and its effect on cellular senescence; (3) Investigate the time course of interactions between mdm2-WRN and mdm2-p53 in response to oxidative stress; (4) Examine WRN ubiquitination and degradation by mdm2 in cells during DNA damage; (5) Investigate the functional consequence of mdm2 regulation of WRN stability in p53 dependent cellular senescence in response to oxidative stress. Our studies will provide a new insight for cell fate determination in response to various types of stress and reveal the molecular mechanisms underlying WRN-mdm2-p53 in regulation of cellular senescence and aging.

p53激活诱导的细胞衰老是其抑癌机制的重要部分。但p53激活也能够诱导细胞凋亡或生长阻滞。细胞如何选择走向凋亡，生长阻滞或衰老，其机制尚不清楚。Werner综合症是最典型的未老先衰的遗传疾病。此病是由WRN 基因突变引起的，从Werner综合症病人身上获得的细胞与正常细胞相比表现出很严重的复制性衰老性状。本课题组是最早发现WRN能够被泛素化调节并成功地发现mdm2能够泛素化WRN蛋白并缩短其半衰期。我们将继续本课题的如下内容：（1）以体内外的实验确证mdm2是WRN的E3连接酶并调查在细胞中WRN泛素化和降解的调节机制及对衰老的影响；（2）调查在应激情况下，mdm2-WRN和mdm2-p53结合的调节；细胞中mdm2泛素化及降解WRN的情况；mdm2调节WRN的稳定性在p53依赖的细胞衰老过程中的功能。本研究将增加我们对细胞衰老激发机制的理解，并且在改善和防止衰老方面具有潜在作用。

p53激活诱导的细胞衰老是其抑癌机制的重要部分。但p53激活也能够诱导细胞凋亡或生长阻滞。细胞如何选择走向凋亡，生长阻滞或衰老，其机制尚不清楚。Werner综合症是最典型的未老先衰的遗传疾病。此病是由WRN 基因突变引起的，从Werner综合症病人身上获得的细胞与正常细胞相比表现出很严重的复制性衰老性状。本课题组从早其发现WRN能够被泛素化调节并成功地发现mdm2能够泛素化WRN蛋白并缩短其半衰期出发，深入研究了p53-mdm2-WRN的调节关系，发现在正常情况下，mdm2主要与p53结合并控制其泛素化及降解。而在应激情况下，p53与mdm2分离，p53得到稳定并激活，从而调节其下游靶基因的表达。而分离出来的mdm2则与WRN结合，从而导致其泛素化并降解。这样的结果导致了细胞中富含稳定并激活的p53而WRN蛋白则显著减少，从而使细胞走向衰老。研究证明了mdm2和WRN在调控p53依赖的细胞衰老中的精确作用，并进一步阐明了WRN-mdm2-p53结合在诱导细胞衰老中的分子机制，对细胞在应对各种不同的应激情况下如何决定细胞命运提供新的理解。