Department of Cancer Biology and Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
PLoS One. 2013;8(2):e55813. doi: 10.1371/journal.pone.0055813. Epub 2013 Feb 6.
p53 plays a central role in tumor suppression. It does so by inducing anti-proliferative processes as a response to various tumor-promoting stresses. p53 is regulated by the ubiquitin ligase Mdm2. The optimal function of Mdm2 requires Daxx, which stabilizes Mdm2 through the deubiquitinase Hausp/USP7 and also directly promotes Mdm2's ubiquitin ligase activity towards p53. The Daxx-Mdm2 interaction is disrupted upon DNA damage. However, both the mechanisms and the consequence of the Daxx-Mdm2 dissociation are not understood. Here we show that upon DNA damage Daxx is phosphorylated in a manner that is dependent on ATM, a member of the PI 3-kinase family that orchestrates the DNA damage response. The main phosphorylation site of Daxx is identified to be Ser564, which is a direct target of ATM. Phosphorylation of endogenous Daxx at Ser564 occurs rapidly during the DNA damage response and precedes p53 activation. Blockage of this phosphorylation event prevents the separation of Daxx from Mdm2, stabilizes Mdm2, and inhibits DNA damage-induced p53 activation. These results suggest that phosphorylation of Daxx by ATM upon DNA damage disrupts the Daxx-Mdm2 interaction and facilitates p53 activation.
p53 在肿瘤抑制中起着核心作用。它通过诱导抗增殖过程来响应各种促进肿瘤的应激。p53 受泛素连接酶 Mdm2 的调节。Mdm2 的最佳功能需要 Daxx，Daxx 通过去泛素酶 Hausp/USP7 稳定 Mdm2，并直接促进 Mdm2 对 p53 的泛素连接酶活性。在 DNA 损伤时，Daxx-Mdm2 相互作用被破坏。然而，Daxx-Mdm2 解离的机制和后果尚不清楚。在这里，我们表明，在 DNA 损伤后，Daxx 以一种依赖于 ATM 的方式被磷酸化，ATM 是参与 DNA 损伤反应的 PI3 激酶家族的成员。Daxx 的主要磷酸化位点被鉴定为 Ser564，这是 ATM 的直接靶标。内源性 Daxx 在 Ser564 的磷酸化在 DNA 损伤反应中迅速发生，并先于 p53 的激活。阻断这一磷酸化事件可防止 Daxx 与 Mdm2 分离，稳定 Mdm2，并抑制 DNA 损伤诱导的 p53 激活。这些结果表明，ATM 在 DNA 损伤后对 Daxx 的磷酸化破坏了 Daxx-Mdm2 相互作用，促进了 p53 的激活。
