Regulation of the ATM/ATR-p53 DNA Damage Signaling Pathway by the Wip1 Phosphatas

描述（由申请人提供）：肿瘤抑制因子p53通过其拮抗剂Mdm2、Mdm4和COP1的受控降解负调控，具有高转复率和低生理水平。在DNA损伤胁迫下，p53迅速稳定下来，并通过转录调节一系列介导细胞周期阻滞、细胞衰老、DNA修复和细胞凋亡的基因。越来越多的证据表明，ATM/ atr介导的Mdm2、Mdm4和COP1的磷酸化加速了它们的降解，这可能是早期DNA损伤反应中诱导p53的初始驱动力。当细胞在DNA修复后恢复到正常状态时，p53需要同时减少。我们对修复后DNA损伤反应如何“失活”知之甚少。最近的证据表明，一种新的蛋白磷酸酶Wip1（或PPM1D）有助于关闭由ATM/ATR激酶启动的激活环，从而为p53提供稳态调节。我们的初步结果表明，Wip1通过去磷酸化其ATM靶向Ser395来稳定Mdm2，导致p53水平下降。我们还发现Wip1在体外使Mdm4和COP1的ATM靶向位点去磷酸化。如果异常调节，Wip1成为一种致癌磷酸酶，抑制ATM/ATR DNA损伤反应和p53肿瘤抑制途径。Wip1基因在许多表达野生型p53的人类癌症中被扩增，这表明它在肿瘤进展中具有致癌功能。Wip1基因敲除小鼠对自发性肿瘤具有抗性，这与p53活性上调一致。待验证的假设是Wip1主要通过在ATM/ATR DNA损伤反应通路中去磷酸化其拮抗剂（Mdm2， Mdm4和COP1）来调节p53。

DESCRIPTION (provided by applicant): Negatively regulated by controlled degradation through its antagonists including Mdm2, Mdm4 and COP1, the tumor suppressor p53 have a high turn-around rate and low physiological levels. Upon DNA damage stress, p53 is rapidly stabilized and transcriptionally regulates a broad array of genes that mediate cell cycle arrest, cellular senescence, DNA repair, and apoptosis. Accumulating evidence suggests that ATM/ATR-mediated phosphorylation of Mdm2, Mdm4 and COP1 accelerates their degradation, which may be the initial driving force to induce p53 during the early DNA damage response. When the cell returns to its normal state following DNA repair, p53 needs to be simultaneously reduced. Very little is known about how the DNA damage response is `deactivated' following repair. Recent evidence suggests that a novel protein phosphatase, Wip1 (or PPM1D), contributes to closing the activation loop initiated by ATM/ATR kinases to provide p53 a homeostatic regulation. Our preliminary results showed that Wip1 stabilizes Mdm2 by dephosphorylating its ATM targeted Ser395, resulting in decreased levels of p53. We also showed that Wip1 dephosphorylates Mdm4 and COP1 in vitro at their ATM targeting sites. If aberrantly regulated, Wip1 becomes an oncogenic phosphatase that inhibits ATM/ATR DNA damage response and p53 tumor suppressor pathways. The Wip1 gene is amplified in a number of human cancers expressing wildtype p53, suggesting it possesses oncogenic functions in tumor progression. Wip1 knockout mice are resistant to spontaneous tumors, consistent with their up-regulated p53 activity. The hypothesis to be tested is that Wip1 regulates p53 primarily through dephosphorylating its antagonists (Mdm2, Mdm4 and COP1) in the ATM/ATR DNA damage response pathway.