Wang Zhiwei, Inuzuka Hiroyuki, Zhong Jiateng, Fukushima Hidefumi, Wan Lixin, Liu Pengda, Wei Wenyi
Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
Oncotarget. 2012 Sep;3(9):1026-35. doi: 10.18632/oncotarget.640.
The Mdm2 oncoprotein promotes p53 ubiquitination and destruction. Yet, exact molecular mechanisms of Mdm2 destruction itself, under DNA damaging conditions, remain unclear. Recently, we identified SCFβ-TRCP as a novel E3 ligase that targets Mdm2 for ubiquitination and destruction in a Casein Kinase Iδ (CKIδ)-dependent manner. However, it remains elusive how the β-TRCP/CKIδ/Mdm2 signaling axis is regulated by DNA damage signals to govern p53 activity. Consistent with previous studies, we found that inactivation of the Ataxia Telangiectasia Mutated (ATM) kinase, in turn, impaired DNA damage-induced Mdm2 destruction. Although phosphorylation of Mdm2 at Ser395 (an ATM phosphorylation site) facilitated Mdm2 interaction with β-TRCP, Ser395A-Mdm2 was degraded non-distinguishably from WT-Mdm2 by SCFβ-TRCP upon DNA damaging treatments. This indicates that in addition to phosphorylating Mdm2 at Ser395, ATM may govern Mdm2 stability through other unknown mechanisms. We further demonstrated that DNA damage-induced activation of ATM directly phosphorylated CKIδ at two well-conserved S/TQ sites, which promotes CKIδ nuclear localization to increase CKIδ-mediated phosphorylation of Mdm2, thereby facilitating subsequent Mdm2 ubiquitination by SCFβ-TRCP. Our studies provide a molecular mechanism of how ATM could govern DNA damage-induced destruction of Mdm2 in part by phosphorylating both Mdm2 and CKIδ to modulate SCFβ-TRCP-mediated Mdm2 ubiquitination. Given the pivotal role of Mdm2 in the negative regulation of p53, this work will also provide a rationale for developing CKIδ or ATM agonists as anti-cancer agents.
Mdm2癌蛋白可促进p53的泛素化及降解。然而，在DNA损伤条件下，Mdm2自身降解的确切分子机制仍不清楚。最近，我们鉴定出SCFβ-TRCP是一种新型E3连接酶，它以酪蛋白激酶Iδ（CKIδ）依赖的方式靶向Mdm2进行泛素化及降解。然而，β-TRCP/CKIδ/Mdm2信号轴如何受DNA损伤信号调控以控制p53活性仍不清楚。与之前的研究一致，我们发现共济失调毛细血管扩张突变（ATM）激酶失活反过来会损害DNA损伤诱导的Mdm2降解。尽管Mdm2的Ser395位点（一个ATM磷酸化位点）磷酸化促进了Mdm2与β-TRCP的相互作用，但在DNA损伤处理后，SCFβ-TRCP对Ser395A-Mdm2的降解与野生型Mdm2并无差异。这表明，除了在Ser395位点磷酸化Mdm2外，ATM可能通过其他未知机制控制Mdm2的稳定性。我们进一步证明，DNA损伤诱导的ATM激活直接在两个保守的S/TQ位点磷酸化CKIδ，这促进了CKIδ的核定位，以增加CKIδ介导的Mdm2磷酸化，从而促进随后SCFβ-TRCP介导的Mdm2泛素化。我们的研究提供了一种分子机制，即ATM如何通过磷酸化Mdm2和CKIδ来部分控制DNA损伤诱导的Mdm2降解，从而调节SCFβ-TRCP介导的Mdm2泛素化。鉴于Mdm2在p53负调控中的关键作用，这项工作也将为开发CKIδ或ATM激动剂作为抗癌药物提供理论依据。
