Shen Hong, Moran Diarmuid M, Maki Carl G
Department of Radiation Oncology, University of Chicago, Chicago, Illinois60637, USA.
Cancer Res. 2008 Oct 15;68(20):8260-8. doi: 10.1158/0008-5472.CAN-08-1901.
p53 Activity is controlled in large part by MDM2, an E3 ubiquitin ligase that binds p53 and promotes its degradation. The MDM2 antagonist Nutlin-3a stabilizes p53 by blocking its interaction with MDM2. Several studies have supported the potential use of Nutlin-3a in cancer therapy. Two different p53 wild-type cancer cell lines (U2OS and HCT116) treated with Nutlin-3a for 24 hours accumulated 2N and 4N DNA content, suggestive of G(1) and G(2) phase cell cycle arrest. This coincided with increased p53 and p21 expression, hypophosphorylation of pRb, and depletion of Cyclin B1, Cyclin A, and CDC2. Upon removal of Nutlin-3a, 4N cells entered S phase and re-replicated their DNA without an intervening mitotic division, a process known as endoreduplication. p53-p21 pathway activation was required for the depletion of Cyclin B1, Cyclin A, and CDC2 in Nutlin-3a-treated cells and for endoreduplication after Nutlin-3a removal. Stable tetraploid clones could be isolated from Nutlin-3a treated cells, and these tetraploid clones were more resistant to ionizing radiation and cisplatin-induced apoptosis than diploid counterparts. These data indicate that transient Nutlin-3a treatment of p53 wild-type cancer cells can promote endoreduplication and the generation of therapy-resistant tetraploid cells. These findings have important implications regarding the use of Nutlin-3a in cancer therapy
p53的活性在很大程度上受MDM2调控，MDM2是一种E3泛素连接酶，它与p53结合并促进其降解。MDM2拮抗剂Nutlin-3a通过阻断p53与MDM2的相互作用来稳定p53。多项研究支持了Nutlin-3a在癌症治疗中的潜在用途。用Nutlin-3a处理24小时的两种不同的p53野生型癌细胞系（U2OS和HCT116）积累了2N和4N的DNA含量，提示G1期和G2期细胞周期阻滞。这与p53和p21表达增加、pRb的低磷酸化以及细胞周期蛋白B1、细胞周期蛋白A和细胞周期蛋白依赖性激酶2（CDC2）的消耗同时发生。去除Nutlin-3a后，4N细胞进入S期并重新复制其DNA，而没有中间的有丝分裂，这一过程称为核内复制。在Nutlin-3a处理的细胞中，细胞周期蛋白B1、细胞周期蛋白A和CDC2的消耗以及去除Nutlin-3a后的核内复制需要p53-p21途径的激活。可以从Nutlin-3a处理的细胞中分离出稳定的四倍体克隆，并且这些四倍体克隆比二倍体对应物对电离辐射和顺铂诱导的凋亡更具抗性。这些数据表明，对p53野生型癌细胞进行短暂的Nutlin-3a处理可以促进核内复制并产生抗治疗的四倍体细胞。这些发现对于Nutlin-3a在癌症治疗中的应用具有重要意义。
