From the Department of Radiation Oncology, Lineberger Comprehensive Cancer Center and.
the Jiangsu Center for the Collaboration and Innovation of Cancer Biotherapy, Cancer Institute, Xuzhou Medical University, Xuzhou, Jiangsu 221002, China.
J Biol Chem. 2017 Dec 29;292(52):21614-21622. doi: 10.1074/jbc.RA117.000122. Epub 2017 Nov 9.
The MDM2 RING domain harbors E3 ubiquitin ligase activity critical for regulating the degradation of tumor suppressor p53, which controls many cellular pathways. The MDM2 RING domain also is required for an interaction with MDMX. Mice containing a substitution in the MDM2 RING domain, MDM2, disrupting MDM2 E3 function and the MDMX interaction, die during early embryogenesis that can be rescued by p53 deletion. To investigate whether MDM2, which retains p53 binding, has p53-suppressing activity, we generated ; mice, in which we replaced the endogenous alleles with an inducible allele, and compared survival with that of similarly generated ; mice. Adult -null mice died ∼7 days after tamoxifen-induced p53 activation, indicating that in the absence of MDM2, MDMX cannot suppress p53. Surprisingly, ; mice died ∼5 days after tamoxifen injection, suggesting that p53 activity is higher in the presence of MDM2 than in the absence of MDM2. Indeed, in MDM2-expressing mouse tissues and embryonic fibroblasts, p53 exhibited higher transcriptional activity than in those expressing no MDM2 or no MDM2 and MDMX. This observation indicated that MDM2 not only is unable to suppress p53 but may have gained the ability to enhance p53 activity. We also found that p53 acetylation, a measure of p53 transcriptional activity, was higher in the presence of MDM2 than in the absence of MDM2. These results reveal an unexpected role of MDM2 in enhancing p53 activity and suggest the possibility that compounds targeting MDM2 RING domain function could produce even more robust p53 activation.
MDM2 的 RING 结构域具有 E3 泛素连接酶活性，对于调节肿瘤抑制因子 p53 的降解至关重要，p53 控制着许多细胞途径。MDM2 的 RING 结构域也需要与 MDMX 相互作用。含有 MDM2 RING 结构域替换的突变（MDM2），破坏 MDM2 的 E3 功能和 MDMX 相互作用的小鼠，在早期胚胎发生期间死亡，可通过 p53 缺失挽救。为了研究保留与 p53 结合的 MDM2 是否具有抑制 p53 的活性，我们生成了 ； 小鼠，其中我们用可诱导的 ； 等位基因替换内源性 ； 等位基因，并比较了与类似生成的 ； 小鼠的存活情况。成年 -/- 小鼠在他莫昔芬诱导的 p53 激活后约 7 天死亡，表明在没有 MDM2 的情况下，MDMX 不能抑制 p53。令人惊讶的是， ； 小鼠在他莫昔芬注射后约 5 天死亡，表明在存在 MDM2 的情况下，p53 的活性高于没有 MDM2 的情况下。事实上，在表达 MDM2 的小鼠组织和胚胎成纤维细胞中，p53 的转录活性高于不表达 MDM2 或不表达 MDM2 和 MDMX 的细胞。这一观察结果表明，MDM2 不仅不能抑制 p53，而且可能获得了增强 p53 活性的能力。我们还发现，p53 乙酰化（一种衡量 p53 转录活性的指标）在存在 MDM2 的情况下高于不存在 MDM2 的情况。这些结果揭示了 MDM2 在增强 p53 活性方面的意外作用，并表明靶向 MDM2 RING 结构域功能的化合物可能产生更强烈的 p53 激活。
