Tan Ban Xiong, Khoo Kian Hoe, Lim Tit Meng, Lane David Philip
p53 Laboratory, A-STAR, Singapore.
Oncotarget. 2014 Feb 28;5(4):933-43. doi: 10.18632/oncotarget.1559.
Although p53 is found mutated in almost 50% of all cancers, p53 mutations in leukaemia are relatively rare. Acute myeloid leukaemia (AML) cells employ other strategies to inactivate their wild type p53 (WTp53), like the overexpression of the p53 negative regulators Mdm2 and Mdm4. As such, AMLs are excellent candidates for therapeutics involving the reactivation of their WTp53 to restrict and destroy cancer cells, and the Mdm2 antagonist nutlin-3 is one such promising agent. Using AML cell lines with WTp53, we identified stable and high levels of p53 in the OCI/AML-2 cell lines. We demonstrate that this nutlin-3 sensitive cell line overexpressed Mdm4 to sequester, stabilise and inhibit p53 in the cytoplasm. We also show that elevated Mdm4 competed with Mdm2-p53 interaction and therefore extended p53 half-life while preventing p53 transcriptional activity. Our results provide biochemical evidence on the dynamics of the p53-Mdm2-Mdm4 interactions in affecting p53 levels and activity, and unlike previously reported findings derived from genetically manipulated systems, AML cells with naturally high levels of Mdm4 remain sensitive to nutlin treatment.
Endogenously high levels of Mdm4 inhibit and sequester p53 in AML. High levels of Mdm4 do not block function of Mdm2 inhibitors in AML.
尽管在几乎50%的所有癌症中都发现p53发生了突变，但白血病中的p53突变相对少见。急性髓系白血病（AML）细胞采用其他策略来使野生型p53（WTp53）失活，比如p53负调控因子Mdm2和Mdm4的过表达。因此，AML是涉及重新激活其WTp53以限制和破坏癌细胞的治疗的极佳候选对象，而Mdm2拮抗剂nutlin-3就是这样一种有前景的药物。使用具有WTp53的AML细胞系，我们在OCI/AML-2细胞系中鉴定出稳定且高水平的p53。我们证明，这种对nutlin-3敏感的细胞系过表达Mdm4以在细胞质中隔离、稳定并抑制p53。我们还表明，升高的Mdm4与Mdm2-p53相互作用竞争，因此延长了p53的半衰期，同时阻止了p53的转录活性。我们的结果提供了关于p53-Mdm2-Mdm4相互作用在影响p53水平和活性方面的动态变化的生化证据，并且与先前从基因操作系统得出的报道结果不同，具有天然高水平Mdm4的AML细胞对nutlin治疗仍敏感。
内源性高水平的Mdm4在AML中抑制并隔离p53。高水平的Mdm4不会阻断AML中Mdm2抑制剂的功能。
