Urokinase Receptor-initiated Cell-signaling

描述(申请人提供)：这项研究项目集中在尿激酶受体(UPAR)，一种多功能的GPI锚定的膜蛋白，已牵涉到乳腺癌的进展。我们的长期目标是了解uPAR调节癌细胞生理的机制。UPAR结合至少两个配体：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，Vitronectin。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)横向结合。这些“共受体”的相互作用导致形成一个动态的多蛋白信号受体复合体(MSRC)。UPA和Vitronectin激活uPAR依赖的细胞信号；然而，这两种途径是不同的。UPA结合激活ERK/MAP激酶，而Vitronectin激活Rad。其他信号蛋白，如STAT-5b，可能在uPAR下游招募，这取决于MSRC中与uPAR相关的辅助受体。辅受体也决定了细胞反应的性质，例如uPA是否有丝分裂原。在本申请中，提出了四个具体目标。在目标1中，我们建议阐明从uPAR到rac1的途径，并确定单个受体(UPAR)与两个不同的配体(uPA或Vitronectin)连接导致完全不同的细胞信号反应的机制。目的2基于我们已经证明uPAR过度表达诱导上皮-间充质转化(EMT)的初步数据，这是一个众所周知的与肿瘤进展相关的过程，在这个过程中，上皮细胞呈成纤维细胞样形态，失去细胞与细胞的接触，波形蛋白表达增加，E-钙粘素表达降低。目标2计划的实验将确定uPAR诱导EMT的机制。在目标3中，我们将检验这一假设，即uPAR依赖的细胞信号不仅调节癌细胞对uPA的反应，还调节如EGF和PDGF等生长因子的反应。了解UPAR和RTK之间的串扰是一个关键目标。最后，在目标4中，我们建议进行研究，以确定uPAR依赖的细胞信号是否参与体内癌症的发生和发展。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如何被用于新的癌症治疗设计的关键信息。

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.