Plasminogen activator inhibitor-1 in tumor progression and metastasis

描述（由申请人提供）：血管生成对肿瘤进展至关重要。这一过程是由肿瘤细胞产生的血管生成因子启动的。结果，内皮细胞（EC）离开静止状态，并且令人惊讶地变得对细胞凋亡更敏感。这就提出了一个根本问题，即EC如何规避在血管生成转换过程中启动的促凋亡力量？多年来，已经报道纤溶酶原激活物抑制剂-1（派-1）的水平在癌症的更晚期中矛盾地升高，并且派-1是不良临床结果的指标。派-1可能在血管生成中起刺激作用而不是抑制作用。在我们的实验室中，我们做了两个观察表明派-1可能提供了一个重要的途径，以保护EC凋亡。首先，我们报道了派-1阻止EC附着到玻连蛋白，并在没有细胞凋亡的情况下刺激向纤连蛋白迁移。第二，我们最近证明，通过其细胞外和抗蛋白水解活性，派-1阻止纤溶酶裂解细胞膜相关的Fas配体（mFasL）和释放的21.5 kDa的可溶性促凋亡FasL片段，诱导细胞凋亡EC。基于这些观察结果，将在本研究提案中进行测试的中心假设是，在刺激EC中派-1表达的增加对于保护EC免受FasL/Fas介导的凋亡至关重要。这一假设将通过3个具体目标进行检验。在目的1中，我们将研究21.5 kDa纤溶酶产生的sFasL诱导细胞凋亡的机制，探索派-1是否也可以独立于Fas保护EC免于凋亡，并测试派-1是否通过缺氧（HIF-11）或VEGF的上调对受刺激EC的存活至关重要。在目标2中，我们将在体内测试派-1通过阻止sFasL的释放来控制血管生成以及该过程如何受到缺氧的影响。我们还将确定由骨髓源性细胞和肿瘤细胞产生的派-1对血管生成和转移的贡献。在目标3中，我们将使用药理学方法来检查派-1抑制对肿瘤生长和血管生成的影响。从这些研究中，我们预期一个基本的了解EC逃避FasL/Fas介导的细胞凋亡在血管生成刺激过程中使用的关键机制。公共卫生相关性：纤溶酶原激活物抑制剂-1（派-1）是一种控制血栓溶解的蛋白质。这种蛋白质一直被发现在癌症患者，特别是乳腺癌患者中升高，并且是临床结果不佳的指标。本申请将研究派-1如何积极促进肿瘤血管生成，并检查通过抗体或小分子抑制派-1是否具有治疗价值。由于派-1在癌症以外的其他疾病中起着促进作用，如糖尿病视网膜病变和血栓性疾病，我们的研究将提供有关靶向派-1治疗癌症和其他几种人类疾病的有价值的信息。

DESCRIPTION (provided by applicant): Angiogenesis is critical for tumor progression. This process is initiated by angiogenic factors produced by tumor cells. As a result, endothelial cells (EC) leave a state of quiescence and surprisingly become more sensitive to apoptosis. This raises the fundamental question of how can EC circumvent the pro-apoptotic forces that are initiated during the angiogenic switch? For many years it has been reported that the levels of plasminogen activator inhibitor-1 (PAI-1) are paradoxically elevated in more advanced stages of cancer and that PAI-1 is an indicator of poor clinical outcome. That PAI-1 could play a stimulatory rather than an inhibitory role in angiogenesis has also been suggested. In our laboratory we have made two observations indicating that PAI-1 may provide a critical pathway to protect EC from apoptosis. First we reported that PAI-1 prevents EC attachment to vitronectin and stimulates migration toward fibronectin in the absence of apoptosis. Second, we recently demonstrated that by its extracellular and anti-proteolytic activity, PAI-1 prevents the cleavage by plasmin of cell membrane-associated Fas ligand (mFasL) and the release of a 21.5 kDa soluble pro-apoptotic FasL fragment that induces apoptosis in EC. On the basis of these observations, the central hypothesis that will be tested in this research proposal is that an increase in PAI-1 expression in stimulated EC is critical to protect EC from FasL/Fas-mediated apoptosis. This hypothesis will be tested by 3 specific aims. In Aim 1 we will study the mechanism by which the 21.5 kDa plasmin-generated sFasL induces apoptosis, explore whether PAI-1 could also protect EC from apoptosis independently of Fas and test whether the up-regulation of PAI-1 by hypoxia (HIF-11) or VEGF is critical for the survival of stimulated EC. In Aim 2, we will test in vivo that PAI-1 controls angiogenesis by preventing the release of sFasL and how this process is affected by hypoxia. We will also determine the contribution of PAI-1 produced by bone marrow-derived cells and tumors cells to angiogenesis and metastasis. In Aim 3, we will use a pharmacological approach to examine the effect of PAI-1 inhibition on tumor growth and angiogenesis. From these studies we anticipate a fundamental understanding of a critical mechanism used by EC to escape FasL/Fas mediated apoptosis during angiogenic stimulation. PUBLIC HEALTH RELEVANCE: Plasminogen activator inhibitor-1 (PAI-1) is a protein that controls the dissolution of blood clots. This protein has been consistently found to be elevated in patients with cancer and in particular breast cancer, and is an indicator of poor clinical outcome. This application will study how PAI-1 positively contributes to tumor angiogenesis and examine whether inhibition of PAI-1 by antibodies or small molecules can be of therapeutic value. Because PAI-1 plays a contributory role in other conditions than cancer, like diabetic retinopathy and thrombotic diseases, our studies will provide valuable information in regard to targeting PAI-1 in the treatment not only of cancer but of several other human diseases.