Role of Tip60 in Oncogene-Induced Senescence and Tumor Suppression

描述（由申请人提供）：衰老是一种稳定的增殖停滞形式，历史上与细胞复制潜能耗尽相关。激活的癌基因， 如Ras，可诱导年轻细胞过早衰老。最近的研究表明，像细胞凋亡一样，癌基因诱导的衰老是体内真正的肿瘤抑制机制，在癌症发展过程中需要妥协。然而，负责这一重要的抗肿瘤反应的信号通路知之甚少。本实验室的研究表明，p38 MAPK及其下游底物激酶PRAK在体内外致癌ras诱导的衰老和肿瘤抑制中起关键作用，PRAK可能是一种抑癌蛋白。上一个资助期的研究表明，多功能乙酰转移酶Tip 60对致癌ras诱导的衰老也是必不可少的。进一步的分析揭示了一种新的翻译后修饰级联反应，涉及p38，Tip 60和PRAK，这在致癌ras诱导的衰老中起着至关重要的作用。在被ras激活后，p38通过Thr 158的磷酸化诱导Tip 60的乙酰转移酶活性;激活的Tip 60，其直接与 PRAK反过来通过K364的乙酰化以依赖于Tip 60和PRAK被p38磷酸化的方式诱导PRAK的蛋白激酶活性。这些翻译后修饰分别对Tip 60和PRAK的促衰老功能至关重要。在当前的更新申请中，我们提出研究Tip 60介导的乙酰化诱导PRAK活性和功能的机制（目的1和2），并确定这种新型翻译后修饰级联在小鼠癌症模型中诱导衰老和抑制肿瘤中的作用（目的3）。在目的1中，我们将测试一个假设，即Tip 60介导的乙酰化诱导PRAK活性和功能，通过增强p38对接和/或通过调节其亚细胞定位，2可能不是相互排斥的机制。在目标2中，我们将研究Tip 60介导的乙酰化破坏PRAK蛋白中的自抑制构象，导致PRAK激活的可能性，使用生物化学和结构生物学方法。最后，在目的3中，我们将使用DMBA诱导的皮肤癌发生小鼠模型研究p38-Tip 60-PRAK级联在体内衰老诱导过程中的作用。这些研究将可能揭示调节PRAK和其他类似蛋白激酶活性和功能的新分子机制，并为介导衰老和肿瘤抑制的信号通路提供新的见解。对p38-Tip 60-PRAK级联的体内研究可能会导致靶向衰老途径组分的新型癌症疗法的开发。

DESCRIPTION (provided by applicant): Senescence is a form of stable proliferative arrest historically associated with the exhaustion of replicative potential of cells. Activated oncogenes, such as ras, can induce senescence prematurely in young cells. Recent studies demonstrate that like apoptosis, oncogene-induced senescence is a bona fide tumor suppressing mechanism in vivo, which needs to be compromised during cancer development. However, the signaling pathways responsible for this important anti-tumorigenic response are poorly understood. Studies from our lab indicate that the p38 MAPK and its downstream substrate kinase PRAK play a key role in oncogenic ras-induced senescence and tumor suppression both in vitro and in vivo, and that PRAK is likely to be a tumor suppressor protein. Studies from the last funding period demonstrated that a multifunctional acetyltransferase Tip60 is also essential for oncogenic ras-induced senescence. Further analyses revealed a novel posttranslational modification cascade involving p38, Tip60 and PRAK, which plays an essential role in oncogenic ras-induced senescence. Upon activation by ras, p38 induces the acetyltransferase activity of Tip60 through phosphorylation of Thr158; activated Tip60, which directly interacts with PRAK, in turn induces the protein kinase activity of PRAK through acetylation of K364 in a manner that depends on phosphorylation of both Tip60 and PRAK by p38. These posttranslational modifications are critical for the pro-senescent function of Tip60 and PRAK, respectively. In the current renewal application, we propose to investigate the mechanism by which Tip60-mediated acetylation induces the activity and function of PRAK (Aims 1 and 2), and to determine the role of this novel posttranslational modification cascade in senescence induction and tumor suppression in a murine cancer model (Aim 3). In Aim 1, we will test a hypothesis that Tip60-mediated acetylation induces PRAK activity and function by enhancing p38 docking and/or by modulating its subcellular localization, 2 mechanisms that may not be mutually exclusive. In Aim 2, we will examine a possibility that Tip60-mediated acetylation disrupts the autoinhibitory conformation in the PRAK protein, leading to activation of PRAK, using biochemical and structural biology approaches. Finally in Aim 3, we will investigate the role of the p38-Tip60-PRAK cascade during senescence induction in vivo using the DMBA-induced skin carcinogenesis mouse model. These studies will likely reveal novel molecular mechanisms that regulate the activity and function of PRAK and other similar protein kinases, and provide new insights into signaling pathways mediating senescence and tumor suppression. Investigation of the p38-Tip60-PRAK cascade in vivo may lead to the development of novel cancer therapies targeting components of the senescence pathway.