P38 MAPK in Ras-induced Senescence and Transformation

描述(申请人提供)：p38MAPK通路最初被认为是炎症和应激反应的介质。我们和其他人已经证明，这一途径也参与了肿瘤抑制细胞反应，如癌基因诱导的衰老。癌基因诱导的衰老是一种不可逆的增殖停滞形式，在正常细胞中由癌基因激活而触发，在形态上与细胞老化引起的复制性衰老相同。在这笔赠款的当前资助期内，旨在描绘与衰老有关的p38途径组件的研究表明，p38通过下游底物激酶PRAK发挥作用。进一步的研究表明，p38/PRAK介导的衰老在体内可以抑制小鼠模型中的癌症发展，并且PRAK是一种肿瘤抑制蛋白，在某些类型的人类癌症中是失活的。哺乳动物中存在四种p38亚型(p381、2、3和4)，每种亚型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过程中发挥着根本不同的作用。它们在调节衰老诱导的能力和调节衰老的机制上都不同。虽然p381、3和4在致癌的ras诱导的衰老中是必不可少的，但p382是必不可少的。在关键的异构体中，p383通过在Ser33处磷酸化P53来刺激P53的转录活性，从而在癌基因诱导的衰老中发挥作用。相反，p381通过增加p16INK4A的表达，通过p53依赖的机制介导衰老诱导。在这一更新应用中，我们试图进一步阐明p38亚型在癌基因诱导的衰老中的不同作用机制，并确定p38亚型介导的衰老在癌症发生中的生物学相关性。首先，我们将通过分析p381介导ras诱导p16INK4A表达的机制以及这一调控的功能后果，来研究p381在衰老中的作用。接下来，我们将通过测试p38亚型失活对具有明确基因改变的转化模型细胞系的致瘤表型的影响，来表征p38亚型在细胞培养中的肿瘤抑制活性。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。这项工作的结果将从机制上深入了解p38亚型在癌基因诱导的衰老中的不同作用，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中，作为抗炎药物，拟议的研究将有助于通过确定应该排除为药物靶点的抑制肿瘤的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.