Mdm2 RING mutation enhances p53 transcriptional activity and p53-p300 interaction.
Mdm2 RING mutation enhances p53 transcriptional activity and p53-p300 interaction.
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DOI：
10.1371/journal.pone.0038212
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发表时间：
2012
期刊：
影响因子：
3.7
通讯作者：
Zhang Y
中科院分区：
文献类型：
--
作者：
Clegg HV;Itahana Y;Itahana K;Ramalingam S;Zhang Y
p53转录因子和肿瘤抑制因子主要由E3泛素连接酶Mdm 2调节，其泛素化p53以靶向其进行蛋白酶体降解。除了其泛素连接酶功能之外，Mdm 2被认为能够通过与p53的反式激活结构域结合并掩蔽p53的反式激活结构域来抑制p53的转录活性。2007年的一项研究挑战了Mdm 2通过单独结合而非泛素化来抑制p53活性的能力，该研究使用了在Mdm 2的RING结构域中携带单个半胱氨酸至丙氨酸点突变（C462 A）的敲入小鼠。具有这种突变的小鼠胚胎成纤维细胞不能抑制p53活性，这种突变消除了Mdm 2的E3泛素连接酶活性而不影响其与p53结合的能力。在这项研究中，我们利用Mdm 2C 462 A小鼠模型，进一步详细描述了Mdm 2的RING结构域在p53控制中的作用。在这里，我们在体内表明，Mdm 2C 462 A蛋白不仅不能抑制p53，而且与完全不存在Mdm 2相比，Mdm 2C 462 A实际上增强了p53对p53靶基因p21/CDKN 1A、MDM 2、BAX、NOXA和14-3-3σ的转录活性。此外，我们发现Mdm 2C 462 A促进p53和乙酰转移酶CBP/p300之间的相互作用，并且它不能与其同源物和p53的姐妹调节因子Mdmx异源二聚化，这表明Mdm 2抑制p300-p53相互作用以及与Mdmx相互作用需要完全完整的RING结构域。这些发现有助于我们更好地理解Mdm 2-p53通路的复杂调节，并对靶向Mdm 2的化疗药物具有重要意义，因为它们表明抑制Mdm 2的E3泛素连接酶活性可能足以增加体内p53活性，而不需要阻断Mdm 2-p53结合。
The p53 transcription factor and tumor suppressor is regulated primarily by the E3 ubiquitin ligase Mdm2, which ubiquitinates p53 to target it for proteasomal degradation. Aside from its ubiquitin ligase function, Mdm2 has been believed to be capable of suppressing p53's transcriptional activity by binding with and masking the transactivation domain of p53. The ability of Mdm2 to restrain p53 activity by binding alone, without ubiquitination, was challenged by a 2007 study using a knockin mouse harboring a single cysteine-to-alanine point mutation (C462A) in Mdm2's RING domain. Mouse embryonic fibroblasts with this mutation, which abrogates Mdm2's E3 ubiquitin ligase activity without affecting its ability to bind with p53, were unable to suppress p53 activity. In this study, we utilized the Mdm2C462A mouse model to characterize in further detail the role of Mdm2's RING domain in the control of p53. Here, we show in vivo that the Mdm2C462A protein not only fails to suppress p53, but compared to the complete absence of Mdm2, Mdm2C462A actually enhances p53 transcriptional activity toward p53 target genes p21/CDKN1A, MDM2, BAX, NOXA, and 14-3-3σ. In addition, we found that Mdm2C462A facilitates the interaction between p53 and the acetyltransferase CBP/p300, and it fails to heterodimerize with its homolog and sister regulator of p53, Mdmx, suggesting that a fully intact RING domain is required for Mdm2's inhibition of the p300-p53 interaction and for its interaction with Mdmx. These findings help us to better understand the complex regulation of the Mdm2-p53 pathway and have important implications for chemotherapeutic agents targeting Mdm2, as they suggest that inhibition of Mdm2's E3 ubiquitin ligase activity may be sufficient for increasing p53 activity in vivo, without the need to block Mdm2-p53 binding.
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