Identification of Novel Protein Phosphatases in the ATM Signaling Pathway

描述（由申请人提供）：当DNA损伤应激时，ATM激酶迅速磷酸化并被激活，从而刺激细胞周期阻滞、细胞衰老、DNA修复和凋亡。当细胞在DNA修复后恢复正常状态时，ATM信号通路需要同时被抑制。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，蛋白磷酸酶有助于关闭由ATM/ATR激酶启动的激活环，以提供稳态调节。我们的初步结果表明，野生型p53诱导的磷酸酶1 （Wip1）通过使几个ATM靶向蛋白去磷酸化来抑制ATM-p53通路。特别是，Wip1通过去磷酸化Mdm2和MdmX的ATM磷酸化位点来稳定它们，从而降低p53的水平和活性。如果受到异常调控，Wip1会成为一种致癌磷酸酶，抑制DNA损伤反应和p53肿瘤抑制途径。我们建立了一个人类丝氨酸/苏氨酸蛋白磷酸酶的表达文库，从中确定了几个新的磷酸酶作为ATM-p53通路的潜在调节剂。待验证的假设是，Wip1和其他抑制性蛋白磷酸酶可能主要通过去磷酸化和稳定Mdm2和MdmX来抑制DNA损伤诱导的p53活性。

DESCRIPTION (provided by applicant): Upon DNA damage stress, the ATM kinase is rapidly phosphorylated and activated, which stimulates cell cycle arrest, cellular senescence, DNA repair, and apoptosis. When the cell is returning to its normal state following DNA repair, the ATM signaling pathway needs to be simultaneously inhibited. Very little is known about how the DNA damage response is 'deactivated' following repair. Recent evidence suggests that protein phosphatases contribute to closing the activation loop initiated by the ATM/ATR kinases to provide a homeostatic regulation. Our preliminary results showed that wildtype p53-induced phosphatase 1 (Wip1) inhibits ATM-p53 pathway by dephosphorylating several ATM targeted proteins. In particular, Wip1 stabilizes Mdm2 and MdmX by dephosphorylating their ATM phosphorylation site, resulting in decreased levels and activity of p53. If aberrantly regulated, Wip1 becomes an oncogenic phosphatase that inhibits the DNA damage response and p53 tumor suppressor pathways. We generated an expression library of human serine/threonine protein phosphatases, from which several novel phosphatases were identified as potential modulators in the ATM-p53 pathway. The hypothesis to be tested is that Wip1 and other inhibitory protein phosphatases may suppress DNA damage-induced p53 activity primarily through dephosphorylating and stabilizing Mdm2 and MdmX. PUBLIC HEALTH RELEVANCE: Protein phosphatases remove phosphate from proteins and deactivate them, which may provide a homeostatic regulation in the DNA damage response pathway. The goal of this research project is to (1) clarify the functions of protein phosphatases in the ATM (Ataxia Telangiectasia Mutated) initiated DNA damage response pathway; (2) determine how protein phosphatases regulate DNA damage-induced p53 activity.