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力的耗尽有关。激活的致癌基因， 例如ras，可以在年轻的细胞中诱导过早衰老。最近的研究表明，与细胞凋亡一样，癌基因诱导的衰老是体内一种真正的肿瘤抑制机制，在癌症发展过程中需要加以折衷。然而，负责这一重要的抗肿瘤反应的信号通路却知之甚少。本实验室的研究表明，p38MAPK及其下游底物激酶PRAK在体外和体内ras诱导的肿瘤衰老和肿瘤抑制中起关键作用，PRAK可能是一种肿瘤抑制蛋白。上一次资助期的研究表明，多功能乙酰转移酶Tip60在致癌的ras诱导的衰老中也是必不可少的。进一步的分析揭示了涉及p38、Tip60和PRAK的新的翻译后修饰级联，它在致癌的ras诱导的衰老中发挥了重要作用。当被ras激活时，p38通过磷酸化Thr158来诱导Tip60的乙酰转移酶活性；激活的Tip60直接与 PRAK通过K364的乙酰化诱导PRAK的蛋白激酶活性，这种方式依赖于p38对Tip60和PRAK的磷酸化。这些翻译后修饰分别对Tip60和PRAK的促衰老功能至关重要。在当前的更新应用中，我们建议研究Tip60介导的乙酰化诱导PRAK(AIMS 1和2)活性和功能的机制，并在小鼠癌症模型中确定这一新的翻译后修饰级联在诱导衰老和抑制肿瘤中的作用(AIM 3)。在目标1中，我们将检验一个假设，即Tip60介导的乙酰化通过促进p38对接和/或通过调节其亚细胞定位来诱导PRAK的活性和功能，这两种机制可能不是相互排斥的。在目标2中，我们将利用生化和结构生物学的方法，研究Tip60介导的乙酰化破坏PRAK蛋白的自抑制构象，导致PRAK激活的可能性。最后，在目标3中，我们将利用DMBA诱导的小鼠皮肤癌变模型，研究p38-Tip60-PRAK级联信号在体内衰老诱导过程中的作用。这些研究可能会揭示调节PRAK和其他类似蛋白激酶活性和功能的新的分子机制，并为调节衰老和肿瘤抑制的信号通路提供新的见解。对体内p38-Tip60-PRAK级联的研究可能会导致针对衰老途径组件的新癌症治疗的发展。

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.