Rac1 GTPase in tumorigenesis and progression of pancreatic cancer

 描述（由申请方提供）：K-Ras基因的激活突变是在人胰腺癌（PC）标本中检测到的最早和最常见的遗传改变，与进展和转移相关。在PC的基因工程小鼠模型（GEMM）中，致癌K-Ras驱动胰腺上皮内瘤变（PanIN病变）的形成及其进展为侵袭性PC。致癌性K-Ras至少具有四种在恶性转化中发挥不同作用的效应子途径：MAPK途径（促分裂原活化蛋白激酶）、PI 3 K途径（磷酸肌醇3-激酶）、Ral-GDS（Ral鸟嘌呤核苷酸解离刺激剂）和Rac 1 GTdR（Ras相关C3肉毒杆菌毒素底物1）。在这些效应器中，最不了解的是Rac 1途径。然而，这条途径最近被证明是至关重要的Ras驱动的PC开发。在转化试验中，Rac 1是Ras癌基因转化所需的，Rac 1的激活突变体可以与MAPK途径合作引发恶性转化。然而，Rac 1促进锚定非依赖性生长和致瘤性的具体机制仍然不清楚，因此负责其与MAPK通路合作的机制也不清楚。本提案的目的是阐明这些机制。我们的中心假设是Rac 1和MAPK通路联合作用以控制在整合来自细胞-细胞和细胞-基质相互作用的信号中起关键作用的蛋白质的表达/活性，最显著的是雅普蛋白（Yes相关蛋白1）。该假设基于表明Rac 1或MAPK途径的抑制导致雅普蛋白降解的初步数据。雅普是一种转录辅激活因子，控制参与增殖的基因。雅普的稳定性、定位和活性受参与感知细胞-细胞和细胞-基质相互作用的信号传导途径（例如Hippo和Wnt途径）控制。在Ras驱动PC的GEMM中，PanIN病变的形成及其进展为侵袭性PC需要雅普。在我们的端粒酶永生化的人胰腺导管细胞中，单独过表达的雅普足以允许锚定非依赖性生长。为了验证我们的中心假设，并明确Rac 1通路在PC的发生和发展中的作用及其与MAPK通路的协同作用，我们提出了三个具体目标：目标1将阐明Rac 1转化活性及其与MAPK通路协同作用的机制;目标2将评估人PC标本中Rac 1活性和雅普水平并评估其病理生物学意义;目的3将阐明Rac 1和MAPK通路在GEMM中PC的启动和进展中的合作和相对贡献。总而言之，拟议的工作将阐明Ras驱动的致癌机制，并揭示新的治疗靶点，这些靶点可能用于治疗胰腺癌和其他Ras驱动的恶性肿瘤。

 DESCRIPTION (provided by applicant): Activating mutations in the K-Ras gene are the earliest and most common genetic alterations detected in human pancreatic cancer (PC) specimens and are associate with progression and metastasis. In genetically engineered mouse models (GEMMs) of PC, oncogenic K-Ras drives the formation of pancreatic intraepithelial neoplasia (PanIN lesions) and their progression to invasive PC. Oncogenic K-Ras has, at least, four effector pathways that play distinct roles in malignant transformation: MAPK pathway (mitogen-activated protein kinase), PI3K pathway (phosphoinositide 3-kinase), Ral-GDS (Ral guanine nucleotide dissociation stimulator), and Rac1 GTPase (Ras-related C3 botulinum toxin substrate 1). Among these effectors, the least well understood is the Rac1 pathway. Yet, this pathway has recently been shown to be critical for Ras-driven PC development. In transformation assays, Rac1 is required for transformation by the Ras oncogenes, and activated mutants of Rac1 can cooperate with the MAPK pathway to elicit malignant transformation. However, the specific mechanisms by which Rac1 promotes anchorage-independent growth and tumorigenicity are still unclear, so are the mechanisms responsible for its cooperation with the MAPK pathway. The objective of this proposal is to elucidate these mechanisms. Our central hypothesis is that the Rac1 and MAPK pathways act conjointly to control the expression/activity of proteins that play critical roles in integrating signals from cell-cell and ell-matrix interactions, most notably the YAP protein (Yes-associated protein 1). This hypothesis is based on preliminary data indicating that the inhibition of either Rac1 or MAPK pathway causes the degradation of the YAP protein. YAP is a transcriptional co-activator that controls genes involves in proliferation. The stability, location, and activity of YAP is controlled by signaling pathways involved in sensing cell-cell and cell-matrix interactions, such as the Hippo and Wnt pathways. In GEMMs of Ras-driven PC, YAP is required for the formation of PanIN lesions and their progression to invasive PC. In our telomerase-immortalized human pancreatic ductal cells, overexpressed YAP alone is sufficient to allow anchorage-independent growth. To test our central hypothesis and define the role of the Rac1 pathway in the initiation and progression of PC and its cooperation with the MAPK pathway, we propose three Specific Aims: Aim 1 will elucidate the mechanisms responsible for the transforming activity of Rac1 and its cooperation with the MAPK pathway; Aim 2 will evaluate Rac1 activity and YAP levels in human PC specimens and assess their pathobiological significance; and Aim 3 will delineate the cooperation and relative contributions of Rac1 and MAPK pathways in the initiation and progression of PC in GEMMs. Altogether, the proposed work will shed light on the mechanisms underlying Ras-driven carcinogenesis and reveal novel therapeutic targets, which could potentially be exploited for the treatment of pancreatic cancers and other Ras-driven malignancies.