Department of Pharmacology and Therapeutics, Buffalo, New York, United States of America.
Flow and Image Cytometry Shared Resource, Buffalo, New York, United States of America.
PLoS Genet. 2022 May 19;18(5):e1010171. doi: 10.1371/journal.pgen.1010171. eCollection 2022 May.
MDM2 and MDM4 are key regulators of p53 and function as oncogenes when aberrantly expressed. MDM2 and MDM4 partner to suppress p53 transcriptional transactivation and polyubiquitinate p53 for degradation. The importance of MDM2 E3-ligase-mediated p53 regulation remains controversial. To resolve this, we generated mice with an Mdm2 L466A mutation that specifically compromises E2 interaction, abolishing MDM2 E3 ligase activity while preserving its ability to bind MDM4 and suppress p53 transactivation. Mdm2L466A/L466A mice exhibit p53-dependent embryonic lethality, demonstrating MDM2 E3 ligase activity is essential for p53 regulation in vivo. Unexpectedly, cells expressing Mdm2L466A manifest cell cycle G2-M transition defects and increased aneuploidy even in the absence of p53, suggesting MDM2 E3 ligase plays a p53-independent role in cell cycle regulation and genome integrity. Furthermore, cells bearing the E3-dead MDM2 mutant show aberrant cell cycle regulation in response to DNA damage. This study uncovers an uncharacterized role for MDM2's E3 ligase activity in cell cycle beyond its essential role in regulating p53's stability in vivo.
MDM2 和 MDM4 是 p53 的关键调节因子，当异常表达时，它们作为癌基因发挥作用。MDM2 和 MDM4 合作抑制 p53 的转录激活，并使 p53 发生多聚泛素化降解。MDM2 E3 连接酶介导的 p53 调节的重要性仍然存在争议。为了解决这个问题，我们生成了 L466A 突变的 Mdm2 小鼠，该突变特异性破坏了 E2 相互作用，从而消除了 MDM2 E3 连接酶的活性，同时保留了其与 MDM4 结合和抑制 p53 转录激活的能力。Mdm2L466A/L466A 小鼠表现出 p53 依赖性胚胎致死性，表明 MDM2 E3 连接酶活性对于体内 p53 调节是必不可少的。出乎意料的是，即使在没有 p53 的情况下，表达 Mdm2L466A 的细胞也表现出细胞周期 G2-M 转换缺陷和增加的非整倍性，表明 MDM2 E3 连接酶在细胞周期调控和基因组完整性中发挥着 p53 非依赖性作用。此外，携带 E3 失活的 MDM2 突变体的细胞在应对 DNA 损伤时表现出异常的细胞周期调控。这项研究揭示了 MDM2 的 E3 连接酶活性在细胞周期中的一个未被描述的作用，超出了其在体内调节 p53 稳定性的基本作用。
