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

描述(申请人提供)：通过其拮抗剂MDM2、MDM4和COP1进行受控降解的负面调节，肿瘤抑制基因P53具有高转复率和低生理水平。在DNA损伤应激下，P53迅速稳定，并在转录上调节一系列广泛的基因，这些基因介导细胞周期停滞、细胞衰老、DNA修复和细胞凋亡。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，这可能是在早期DNA损伤反应中诱导P53的最初驱动力。当细胞在DNA修复后恢复到正常状态时，需要同时减少P53。人们对DNA损伤反应在修复后如何“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ATM/ATR激酶启动的激活环，为p53提供动态平衡调节。我们的初步结果表明，Wip1通过使其ATM靶向Ser395去磷酸化来稳定MDM2，导致p53水平下降。我们还发现，Wip1在体外可以在Mdm4和COP1的ATM靶点上使其去磷酸化。如果调控异常，Wip1成为一种致癌的磷酸酶，抑制ATM/ATR DNA损伤反应和P53肿瘤抑制通路。Wip1基因在一些表达野生型p53的人类癌症中被扩增，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肿瘤具有抵抗力，这与它们上调的P53活性一致。需要检验的假设是，Wip1主要通过在ATM/ATR DNA损伤反应通路中使其拮抗剂(MDM2、MDM4和COP1)去磷酸化来调节P53。与公共健康相关：Wip1基因编码一种酶，可以从蛋白质中去除磷酸盐并使其失活。它在包括乳腺癌、卵巢癌、胰腺癌和前列腺癌在内的几种人类癌症中被放大。本研究的目的是(1)阐明Wip1在ATM(共济失调毛细血管扩张症)启动的DNA损伤反应通路中的功能；(2)确定抑制Wip1是否可以挽救共济失调毛细血管扩张症患者ATM缺陷。

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. PUBLIC HEALTH RELEVANCE: The Wip1 gene encodes an enzyme that removed phosphate from proteins and deactivates them. It is amplified in several human cancers including breast cancer, ovary cancer, pancreatic cancer and prostate cancer. The goal of this research project is to (1) clarify the functions of Wip1 in the ATM (Ataxia Telangiectasia Mutated) initiated DNA damage response pathway; (2) determine if inhibiting Wip1 would rescue ATM deficiency in Ataxia Telangiectasia patients.