Tip60 in p38 and PRAK Mediated 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。激活的癌基因，如ras，可以在年轻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一种真正的体内肿瘤抑制机制，需要在癌症发展过程中被破坏。然而，对这种重要的抗肿瘤反应的信号通路了解甚少。我们实验室的研究表明，p38 MAPK及其下游底物激酶PRAK在体外和体内的致癌ras诱导的衰老和肿瘤抑制中起关键作用，PRAK可能是一种肿瘤抑制蛋白。我们的初步数据显示PRAK直接与多功能组蛋白乙酰转移酶Tip60相互作用。进一步的研究表明，Tip60在致癌的ras诱导的衰老中是必不可少的，并且在衰老诱导过程中，Tip60的表达和磷酸化都是被诱导的。此外，在细胞和体外，p38直接磷酸化Tip60上的S155和T158。此外，Tip60的表达增加可增强PRAK的激酶活性，抑制Tip60可降低ras诱导的PRAK在激活位点的磷酸化，提示Tip60-PRAK相互作用对衰老细胞中PRAK的激活起重要作用。总之，这些发现表明Tip60在癌基因诱导的衰老中起着核心作用。我们假设致癌Ras通过p38介导的磷酸化和蛋白稳定激活Tip60，而激活Tip60反过来刺激PRAK的激酶活性，导致诱导肿瘤抑制衰老反应。本应用程序旨在研究Tip60在体外和体内诱导衰老和抑制肿瘤中的作用机制。首先，我们将研究Ras-p38通路对衰老细胞中Tip60的磷酸化、表达和乙酰转移酶活性的调节。其次，分析在ras诱导的衰老过程中，Tip60-PRAK相互作用对各结合伴侣和p53的表达和活性的影响。最后，PRAK和Tip60及其相互作用对衰老诱导和肿瘤抑制的贡献将在体内进行研究，使用由致癌ras驱动肿瘤发展的小鼠癌症模型，以及在衰老诱导癌基因激活突变频率高的人类癌症中。这些研究结果将进一步揭示肿瘤抑制衰老的信号转导通路，并建立Tip60在癌基因诱导的衰老和肿瘤抑制中的作用机制。这项工作可能会导致针对衰老途径的新癌症治疗的发展。公共卫生相关性：本申请中提出的研究旨在研究癌基因诱导衰老的机制，这是一种重要的肿瘤抑制细胞反应，在人类癌症发展过程中被破坏。这些研究集中在蛋白激酶PRAK和乙酰转移酶Tip60上，它们都可能是肿瘤抑制蛋白。这些研究结果将明确介导衰老反应和肿瘤抑制的信号转导途径，并可能导致针对衰老途径的新型癌症治疗的发展。

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. Our preliminary data reveal that PRAK directly interacts with a multifunctional histone acetyltransferase Tip60. Further investigation indicates that Tip60 is essential for oncogenic ras- induced senescence, and that Tip60 expression and phosphorylation are both induced during senescence induction. Moreover, p38 directly phosphorylates Tip60 on S155 and T158 in cells and in vitro. In addition, increased expression of Tip60 enhances the kinase activity of PRAK, and suppression of Tip60 reduces ras- induced phosphorylation of PRAK at the activation site, suggesting that Tip60-PRAK interaction is important for the activation of PRAK in senescent cells. Together, these findings demonstrate that Tip60 plays a central role in oncogene-induced senescence. We hypothesize that oncogenic Ras activates Tip60 through p38-mediated phosphorylation and protein stabilization, and that activated Tip60 in turn stimulates the kinase activity of PRAK, leading to induction of the tumor-suppressing senescence response. This application is designed to investigate the mechanisms underlying the role of Tip60 in senescence induction and tumor suppression in vitro and in vivo. First, regulation of the phosphorylation, expression and acetyltransferase activity of Tip60 by the Ras-p38 pathway in senescent cells will be examined. Second, the impact of Tip60-PRAK interaction on the expression and activity of each binding partner and p53 during ras-induced senescence will be analyzed. Finally, the contribution of PRAK and Tip60 and their interaction to senescence induction and tumor suppression will be examined in vivo, using mouse cancer models in which tumor development is driven by oncogenic ras, and in human cancers with high frequency of activating mutations in senescence-inducing oncogenes. Results from these studies will delineate the signal transduction pathway mediating the tumor suppressive senescence response, and establish the mechanism underlying the role of Tip60 in oncogene- induced senescence and tumor suppression. The proposed work may lead to the development of new cancer therapies targeting the senescence pathway. PUBLIC HEALTH RELEVANCE: Studies proposed in this application are designed to investigate the mechanism of oncogene-induced senescence, an important tumor suppressive cellular response that is disrupted during human cancer development. These studies focus on a protein kinase PRAK and an acetyltransferase Tip60, both of which are likely to be tumor suppressor proteins. Results from these studies will define the signal transduction pathway mediating the senescence response and tumor suppression, and may lead to the development of novel cancer therapies targeting the senescence pathway.