ROLE OF PROTEIN PHOSPHATASES IN THE DNA DAMAGE RESPONSE

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 我们的长期目标是了解蛋白磷酸酶在DNA损伤反应和肿瘤发生过程中调节P53信号通路的作用。在这个提案中，我们将集中在蛋白磷酸酶对MDMX-P53自动调节反馈环的调节。MDMX抑制由DNA损伤或致癌压力诱导的肿瘤抑制基因P53的转录活性。MDMX的过度表达和P53的异常调控导致细胞生长失控，并促进肿瘤的发生。高水平的MDMX与24.6%的各种人类癌症有关。特别是，在18.5%的人类结直肠癌中，MDMX过表达。因此，必须在单元格中严格控制MDMX。最近，我们已经确定Wip1是一种丝氨酸/苏氨酸蛋白磷酸酶，是MDMX的动态平衡调节因子。我们最近的研究表明，Wip1直接在ATM靶向的Ser403上去磷酸化MDMX。Wip1抑制DNA损伤诱导的MDMX泛素化和降解，导致MDMX的稳定和P53活性的降低。除Wip1外，蛋白磷酸酶1(PP1)的三种异构体也被鉴定为MDMX的阳性调节因子。根据这些令人兴奋的发现，我们假设蛋白磷酸酶可能在MDMX-P53途径的调节中发挥生理学作用。因此，我们将使用体内和介绍的方法来系统地研究这一以前未被验证的假设。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our long-term goal is to understand the roles of protein phosphatases in regulating p53 signaling pathway during DNA damage response and tumorigenesis. In this proposal, we will concentrate on the regulation of MdmX-p53 auto-regulatory feedback loop by protein phosphatases. MdmX inhibits the transcriptional activity of the tumor suppressor p53 that is induced by DNA damage or oncogenic stresses. Overexpression of MdmX and aberrant p53 regulation lead to deregulated cell growth and contribute to tumorigenesis. High levels of MdmX associate with 24.6% of various human cancers. In particular, MdmX is overexpressed in 18.5% of human colorectal cancers. Thus, MdmX must be tightly controlled in cells. Recently, we have identified Wip1, a ser/thr protein phosphatase, as a homeostatic regulator of MdmX. Our recent studies demonstrated that Wip1 directly dephosphorylates MdmX at the ATM-targeted Ser403. Wip1 inhibits the DNA damage-induced ubiquitination and degradation of MdmX, leading to the stabilization of MdmX and reduction of p53 activities. In addition to Wip1, three isoforms of Protein Phosphatase 1 (PP1) have also been identified as positive regulators for MdmX. In light of these exciting findings, we hypothesize that protein phosphatases may play a physiological role in the regulation of the MdmX-p53 pathway. Hence, we will use in vivo and intro approaches to systematically investigate this previously untested hypothesis in this proposal.