P38 MAPK in Ras-induced Senescence and Transformation

描述（由申请人提供）：p38 MAPK途径最初被确定为炎症和应激反应的介质。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引发的一种不可逆的增殖停滞形式，其形态与细胞衰老引起的复制性衰老相同。本基金当前资助期的研究旨在描述p38通路中参与衰老的组分，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介导的衰老在体内抑制小鼠模型中的癌症发展，PRAK是一种肿瘤抑制蛋白，在某些类型的人类癌症中失活。哺乳动物中存在四种p38亚型（p381、p2、p3和p4），每一种都由不同的基因编码。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有所不同。虽然p381, 3和4在致癌ras诱导的衰老中是必需的，但p382是可有可无的。在至关重要的同工异构体中，p383通过p53的Ser33磷酸化刺激p53的转录活性，从而促进癌基因诱导的衰老。相比之下，p381通过p53不依赖的机制，通过增加p16INK4A的表达介导衰老。在这项更新应用中，我们寻求进一步描述p38亚型在癌基因诱导的衰老中不同作用的机制，并确定p38亚型在癌症发展中介导的衰老诱导的生物学相关性。首先，我们将通过分析p381介导ras诱导的p16INK4A表达的机制及其调控的功能后果来研究p381在衰老中的功能。接下来，我们将通过测试p38异构体失活对转化模型细胞系的致瘤表型的影响来表征p38异构体在细胞培养中的抑瘤活性。最后，我们将在小鼠皮肤癌变模型中确定p38亚型在癌基因诱导的衰老和体内肿瘤抑制中的作用。本研究的结果将为p38亚型在癌基因诱导的衰老中的不同作用提供机制见解，并确定p38亚型在体内介导癌基因诱导的衰老和肿瘤抑制中的功能。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识别应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。

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.