Urokinase Receptor-initiated Cell-signaling

描述（由申请人提供）：本研究项目的重点是尿激酶受体（uPAR），一种多功能GPI锚定膜蛋白，与乳腺癌进展有关。我们的长期目标是了解uPAR调节癌细胞生理学的机制。uPAR结合至少两种配体：纤溶酶原激活物，尿激酶型纤溶酶原激活物（uPA），和临时细胞外基质蛋白，玻连蛋白。在质膜内，uPAR与整合素、G蛋白偶联受体和受体酪氨酸激酶（RTK）横向缔合。这些“共受体”相互作用导致形成动态的多蛋白信号受体复合物（MSRC）。uPA和玻连蛋白激活uPAR依赖的细胞信号传导;然而，途径是不同的。uPA结合激活ERK/MAP激酶，而玻连蛋白激活Rad。其他信号传导蛋白，如STAT-5 b，可能被募集到uPAR的下游，这取决于与MSRC中uPAR相关的共受体。辅助受体还决定细胞反应的性质，例如uPA是否是促有丝分裂的。在本申请中，提出了四个具体目标。在目的1中，我们建议阐明导致从uPAR到Rac 1的途径，并确定单个受体（uPAR）与两个不同的配体（uPA或玻连蛋白）的连接导致完全不同的细胞信号传导反应的机制。目的2建立在初步数据的基础上，我们已经证明uPAR过表达诱导上皮-间质转化（EMT），这是一种与癌症进展相关的众所周知的过程，其中上皮细胞采用成纤维细胞样形态，失去细胞-细胞接触，表现出波形蛋白表达增加和E-钙粘蛋白表达减少。目标2中计划的实验将确定uPAR诱导EMT的机制。在目标3中，我们将检验uPAR依赖性细胞信号传导不仅调节癌细胞对uPA的反应，而且调节癌细胞对生长因子如EGF和PDGF的反应的假设。了解uPAR和RTK之间的串扰是一个关键目标。最后，在目标4中，我们提出研究以确定uPAR依赖性细胞信号传导是否参与体内癌症的发展和进展。将应用异种移植和自发性肿瘤小鼠模型系统。这些研究将阐明uPAR在癌症中的作用，并提供有关uPAR如何成为新型癌症治疗设计靶点的关键信息。

DESCRIPTION (provided by applicant): This research project focuses on the urokinase receptor (uPAR), a multifunctional GPI-anchored membrane protein that has been implicated in breast cancer progression. Our long-term goal is to understand mechanisms by which uPAR regulates cancer cell physiology. uPAR binds at least two ligands: the plasminogen activator, urokinase-type plasminogen activator (uPA), and the provisional extracellular matrix protein, vitronectin. Within the plasma membrane, uPAR laterally associates with integrins, G-protein coupled receptors, and receptor-tyrosine kinases (RTKs). These "co-receptor" interactions result in the formation of a dynamic, multiprotein signaling receptor complex (MSRC). uPA and vitronectin activate uPAR-dependent cell signaling; however, the pathways are distinct. uPA-binding activates ERK/MAP kinase whereas vitronectin activates Rad. Other signaling proteins, such as STAT-5b, may be recruited downstream of uPAR depending on the co-receptors that associate with uPAR in the MSRC. Co-receptors also determine the nature of the cellular response, such as whether uPA is mitogenic. In this application, four specific aims are proposed. In Aim 1, we propose to elucidate the pathway that leads from uPAR to Rac1 and determine the mechanism by which ligation of a single receptor (uPAR) with two distinct ligands (uPA or vitronectin) causes completely distinct cell signaling responses. Aim 2 builds on preliminary data in which we have demonstrated that uPAR over-expression induces epithelial-mesenchymal transformation (EMT), a well known process associated with cancer progression in which epithelial cells adopt a fibroblast-like morphology, lose cell-cell contacts, demonstrate increased vimentin expression and decreased E-cadherin expression. Experiments planned in Aim 2 will determine the mechanism by which uPAR induces EMT. In Aim 3, we will test the hypothesis that uPAR-dependent cell signaling regulates the response of cancer cells not only to uPA but also to growth factors such as EGF and PDGF. Understanding crosstalk between uPAR and RTKs is a critical objective. Finally, in Aim 4, we propose studies to determine whether uPAR-dependent cell signaling is involved in cancer development and progression in vivo. Xenograft and spontaneous neoplasia mouse-model systems will be applied. These studies will elucidate the role of uPAR in cancer and provide critical information regarding how uPAR may be targeted for novel cancer therapeutics design.