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（包括Mdm 2、Mdm 4和COP 1）的受控降解进行负调控，具有高逆转率和低生理水平。在DNA损伤应激时，p53迅速稳定并转录调节介导细胞周期停滞、细胞衰老、DNA修复和凋亡的广泛基因阵列。越来越多的证据表明，ATM/ATR介导的Mdm 2、Mdm 4和COP 1的磷酸化加速了它们的降解，这可能是在早期DNA损伤反应中诱导p53的初始驱动力。当细胞在DNA修复后恢复正常状态时，需要同时减少p53。关于DNA损伤反应在修复后是如何“失活”的知之甚少。最近的证据表明，一种新的蛋白磷酸酶，Wip 1（或PPM 1D），有助于关闭激活环启动ATM/ATR激酶提供p53的稳态调节。我们的初步研究结果表明，Wip 1稳定Mdm 2通过去磷酸化其ATM靶向Ser 395，导致p53的水平降低。我们还发现Wip 1在体外使Mdm 4和COP 1在其ATM靶向位点脱磷酸化。如果异常调节，Wip 1成为抑制ATM/ATR DNA损伤反应和p53肿瘤抑制通路的致癌磷酸酶。Wip 1基因在许多表达野生型p53的人类癌症中扩增，表明其在肿瘤进展中具有致癌功能。Wip 1基因敲除小鼠对自发性肿瘤具有抗性，这与它们上调的p53活性一致。待检验的假设是Wip 1主要通过在ATM/ATR DNA损伤反应途径中使其拮抗剂（Mdm 2、Mdm 4和COP 1）去磷酸化来调节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.