Identification of Novel Protein Phosphatases in the ATM Signaling Pathway

描述（由申请人提供）：在DNA损伤应激时，ATM激酶迅速磷酸化并活化，刺激细胞周期停滞、细胞衰老、DNA修复和细胞凋亡。当细胞在DNA修复后恢复到正常状态时，ATM信号通路需要同时被抑制。关于DNA损伤反应在修复后如何“失活”，人们知之甚少。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（Wip 1）通过去磷酸化几个ATM靶向蛋白来抑制ATM-p53通路。特别是，Wip 1通过使ATM磷酸化位点去磷酸化来稳定Mdm 2和MdmX，导致p53的水平和活性降低。如果异常调节，Wip 1成为抑制DNA损伤反应和p53肿瘤抑制途径的致癌磷酸酶。我们产生了一个人丝氨酸/苏氨酸蛋白磷酸酶的表达文库，从其中几个新的磷酸酶被确定为潜在的调节剂在ATM-p53途径。有待检验的假设是，Wip 1和其他抑制性蛋白磷酸酶可能主要通过去磷酸化和稳定Mdm 2和MdmX来抑制DNA损伤诱导的p53活性。 公共卫生相关性：蛋白磷酸酶从蛋白质中去除磷酸盐并使其失活，这可能在DNA损伤反应途径中提供稳态调节。本研究的目的是（1）阐明蛋白磷酸酶在ATM（Ataxia Telangiectasia Mutated）启动的DNA损伤反应途径中的功能;（2）确定蛋白磷酸酶如何调节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.