P38 MAPK in Ras-induced Senescence and Transformation

描述（由申请人提供）：p38 MAPK通路最初被鉴定为炎症和应激反应的介导物。我们和其他人已经表明，这一途径也参与肿瘤抑制细胞反应，如癌基因诱导的衰老。癌基因诱导的衰老是正常细胞中癌基因激活后引发的不可逆的增殖停滞形式，其在形态学上与细胞衰老导致的复制性衰老相同。在本基金资助期内的研究，旨在描述参与衰老的p38通路组分，表明p38通过下游底物激酶PRAK起作用。进一步的研究表明，p38/PRAK介导的衰老在小鼠模型中在体内起作用以抑制癌症发展，并且PRAK是在某些类型的人类癌症中失活的肿瘤抑制蛋白。哺乳动物中存在四种p38亚型（p381、2、3和4），每种亚型由不同的基因编码。我们发现这些p38亚型在癌基因诱导的衰老中起着根本不同的作用。它们在介导衰老诱导的能力和介导衰老的机制上都不同。虽然p381，3和4是致癌ras诱导的衰老所必需的，但p382是不可缺少的。在至关重要的同种型中，p383通过在Ser 33处磷酸化p53来刺激p53的转录活性，从而促进癌基因诱导的衰老。相反，p381通过p53非依赖性机制，通过增加p16 INK 4A的表达来介导衰老诱导。在这个更新的应用程序中，我们试图进一步描绘的机制，潜在的癌基因诱导的衰老的p38亚型的不同作用，并确定衰老诱导的p38亚型介导的癌症发展的生物学相关性。首先，我们将研究p381在衰老中的功能，通过分析p381介导ras诱导的p16 INK 4A表达的机制以及这种调节的功能后果。接下来，我们将通过检测p38亚型的失活对具有确定的遗传改变的转化模型细胞系的致瘤表型的影响来表征p38亚型在细胞培养物中的肿瘤抑制活性。最后，我们将在小鼠皮肤癌发生模型中确定p38亚型在癌基因诱导的衰老和体内肿瘤抑制中的作用。从拟议的工作的结果将提供p38异构体在癌基因诱导的衰老中的不同作用的机制的见解，并定义在介导癌基因诱导的衰老和肿瘤抑制在体内的p38异构体的功能。此外，由于p38的药物抑制剂目前正在开发作为抗炎药物，因此拟议的研究将有助于通过确定应被排除作为药物靶点的肿瘤抑制p38亚型来提高这些药物的安全性。 公共卫生相关性：本申请的总体目标是描述p38亚型在癌基因诱导的衰老中的功能，这是一种故障安全的肿瘤抑制细胞反应。这项工作将促进我们对保护人类免受癌症侵害的机制的理解。由于p38抑制剂目前被用作抗炎药物，因此拟议研究的结果将有助于指导设计没有促癌副作用的安全药物，方法是确定应避免作为药物靶点的肿瘤抑制p38亚型。

DESCRIPTION (provided by applicant): The p38 MAPK pathway was initially identified as a mediator of inflammatory and stress responses. We and others have shown that this pathway also participates in tumor suppressing cellular responses such as oncogene-induced senescence. Oncogene-induced senescence is an irreversible form of proliferative arrest triggered upon activation of oncogenes in normal cells, which is morphologically identical to replicative senescence resulted from cellular aging. Studies in the current funding period of this grant, aimed to delineate the p38 pathway components involved in senescence, demonstrates that p38 acts through a downstream substrate kinase PRAK. Further studies reveal that p38/PRAK-mediated senescence operates in vivo to suppress cancer development in murine models, and that PRAK is a tumor suppressor protein that is inactivated in certain types of human cancer. Four p38 isoforms (p381, 2, 3 and 4) exist in mammals, each encoded by a different gene. We found that these p38 isoforms play fundamentally different roles in oncogene- induced senescence. They differ both in their ability to mediate senescence induction and in the mechanism by which they mediate senescence. While p381, 3 and 4 are essential for oncogenic ras-induced senescence, p382 is dispensable. Among the isoforms that are crucial, p383 contributes to oncogene-induced senescence by stimulating the transcriptional activity of p53 via phosphorylation of p53 at Ser33. In contrast, p381 mediates senescence induction through a p53-indepenedent mechanism, by increasing the expression of p16INK4A. In this renewal application, we seek to further delineate the mechanism underlying the differential roles of the p38 isoforms in oncogene-induced senescence, and to determine the biological relevance of senescence induction mediated by the p38 isoforms in cancer development. First, we will investigate the function of p381 in senescence, by analyzing the mechanism by which p381 mediates the ras-induced expression of p16INK4A and the functional consequence of this regulation. Next, we will characterize the tumor suppressing activity of the p38 isoforms in cell culture by testing the effect of inactivation of the p38 isoforms on the tumorigenic phenotypes of transformed model cell lines with defined genetic alterations. Finally, we will determine the role of the p38 isoforms in oncogene-induced senescence and tumor suppression in vivo in a murine skin carcinogenesis model. Results from the proposed work will provide mechanistic insights into the differential roles of the p38 isoforms in oncogene-induced senescence, and define the function of the p38 isoforms in mediating oncogene-induced senescence and tumor suppressing in vivo. Moreover, since pharmaceutical inhibitors of p38 are currently under development as anti-inflammatory drugs, the proposed studies will help improve the safety of these drugs by identifying the tumor-suppressing p38 isoforms that should be excluded as drug targets. PUBLIC HEALTH RELEVANCE: The overall goal of this application is to delineate the function of the p38 isoforms in oncogene-induced senescence, a fail-safe tumor suppressing cellular response. The proposed work will advance our understanding of the mechanisms that protect human being against cancer. Since p38 inhibitors are currently pursued as anti-inflammatory drugs, results from the proposed studies will help guide the design of safe drugs without cancer-promoting side effects, by identifying the tumor-suppressing p38 isoforms that should be avoided as drug targets.