Nutlin-3a对p53-MDM2复合物稳定性影响

Effect of Nutlin-3a on stability of p53-MDM2 complex

p53蛋白是一种与细胞周期停滞和细胞凋亡有关的蛋白质.在受到细胞压力或环境扰动后,p53促进下游多个靶基因的转录,介导肿瘤抑制.MDM2是主要的E3泛素连接酶,也是p53的负调控因子.MDM2可促进p53的泛素化和核输出,抑制p53的抑癌活性.因此MDM2对p53的负调控始终是肿瘤治疗中急切需要解决的问题.Nutlin-3a是被证明可以有效抑制p53-MDM2相互作用的小分子抑制剂.本文使用全原子分子动力学模拟,研究Nutlin-3a对p53-MDM2复合物的稳定性的影响.结果表明,通过引起p53和MDM2间Phe19-Gln72的氢键和Glu17-Lys94的盐桥发生的断裂,Nutlin-3a可以削弱p53和MDM2间的相互作用.我们的工作对Nutlin-3a小分子抑制剂的作用机制进行了说明,揭示了抗癌药物Nutlin-3a介导的p53-MDM2复合物亲和力降低的分子机制,并为针对p53蛋白的有效抗癌治疗提供了理论基础.

P53 is well recognized to be a tumor suppressor protein.In response to the external stress or environmental perturbation,p53 can promote the transcription of various target genes downstream,thus regulating the cell cycle,apoptosis,DNA repair,and angiogenesis.However,the activation of p53 is further activated by another protein,MDM2,which negatively regulates the level of p53 inverse and thus reduces the activation of p53.This phenomenon is a novel potential and promising strategy for cancer therapy,i.e.restoring the activity of p53 pathway through the competitive inhibitors that can occupy the p53-binding site of MDM2 and thus inhibit the interaction between p53 and MDM2.Recently,various kinds of the inhibitors have been designed for this purpose.The Nutlin family is a group of well investigated inhibitors,which shows high efficiency for tumor suppression.Nutlin-3a mimics the MDM2-binding site of p53 essentially,and blocks the binding of MDM2 to p53.Once getting free from MDM2,p53 rapidly accumulates in the nuclei of cancer cells,the p53 target genes and the p53 pathway are activated,thereby resulting in cell-cycle arrest and apoptosis.In our previous papers,we investigated the competition mechanism between Nutlin3 and p53 in vitro by using molecular dynamics simulations.We found that Nutlin3 can bind faster than p53 to prevent p53 from binding to MDM2 when Nutlin-3a and p53 have equal distance from MDM2.Nutlin-3a can also bind to the p53-MDM2 complex to disturb and weaken the interactions between p53 and MDM2.However,the underlying mechanisms of p53-MDM2 complex instability in vivo are still unclear.And these inhibitors also have a variety of specificities and biological toxicities in vivo environment.In this study,we go a further step to investigate the effect of Nutlin-3a on the stability of p53-MDM2 complex in physiological environment with the aid of the molecular mechanics/generalized borne surface area(MM/GBSA)method.In our simulations,a group of Nutlin-3a molecules are randomly put around the p53 binding pocket of MDM2 in the initial stages to examine the dynamics among p53,MDM2 and the group of Nutlin-3a molecules and to analyze the underlying competition mechanism between Nutlin3 and p53 binding to pocket of MDM2.We find that Nutlin-3a can induce the centroid distance between p53 and MDM2 to increase.Importantly,we show that Nutlin-3a weakens the binding affinity of p53-MDM2 complex.Consistently,Nutlin-3a breaks a hydrogen bond between Phe19-Gln72 and a salt bridge between Glu17-Lys94,which weakens the interactions between p53 and MDM2.From the systematic biology point of view,the regulation of p53 by MDM2 is extremely sensitive to the strength of the p53-MDM2 interaction.The avianization of the interactions between p53 and MDM2 by Nutlin-3a can promote p53 to restore its suppression functions on tumor development.This study may be helpful in understanding the molecular mechanisms of p53-MDM2 complex instability mediated by Nutlin-3a and also in searching for the effective inhibitors of p53-MDM2 interaction.