Lipid Signaling in Chemotaxis

 描述(由申请人提供)：定向细胞向趋化剂迁移，称为趋化性，是许多生理事件的中心，如轴突引导、伤口愈合和组织形态发生。不适当的趋化性是许多人类疾病的主要特征，包括肿瘤转移、哮喘、关节炎和动脉粥样硬化。因此，了解趋化机制对于了解这些趋化相关疾病是至关重要的。我们研究的长期目标是揭示细胞如何感知它们的化学环境并控制它们的迁移行为。我们以变形链藻作为我们的发现工具，以人类细胞为翻译工具，重点研究了细胞内强大的信号磷脂酰肌醇-3，4，5-三磷酸(PIP3)，它产生于细胞的前沿，重组肌动蛋白的细胞骨架。趋化作用领域中一个重要但尚未回答的问题是，细胞如何稳定地维持信号网络，并在趋化物质梯度中重塑肌动蛋白细胞骨架。为了解决这个根本问题，我们目前的研究确定：i)通过持续定位RAS的激活和PIP3的产生来稳定定向感知的信号步骤；ii)直接与PIP3和肌动蛋白细胞骨架结合的分子链接；以及iii)在网柄苔藓和人类中通过将PIP3磷酸酶PTEN移位到质膜来关闭PIP3信号的保守过程。在下一个资助阶段，我们建议研究这些调控事件中的每一个，以及趋化信号高精度控制细胞迁移的机制。在目标1中，我们将确定定向传感是如何在空间上定向到化学诱导剂的。我们假设，发生在细胞前部的Ras GTP酶和PIP3的激活是由位于后端的活性Rho GTP酶通过化学梯度调节的。我们将研究Rho GTP酶是如何向RAS GTP酶传递信号的。在目标2中，我们将确定PIP3结合的单体肌球蛋白I如何将PIP3信号转化为肌动蛋白细胞骨架。我们将测试肌球蛋白I在细胞骨架重塑中的功能的三个模型：将肌动蛋白细丝连接到质膜、直接聚合肌动蛋白和招募肌动蛋白成核因子。在目标3中，我们将描述人PTEN是如何被招募到质膜上的。我们假设，在人类细胞中，质膜上先前未知的PTEN受体介导了这一过程。我们将研究新发现的人PTEN结合蛋白在PTEN定位中的作用。此外，我们还将进一步确定受体在PIP3信号转导中的功能重要性。我们的研究成果有望为趋化作用中的两个核心事件-定向感知和细胞骨架重排-提供一个概念性突破，并可能导致基于趋化作用的癌症和炎症治疗的发展。

 DESCRIPTION (provided by applicant): Directed cell migration toward chemoattractants, termed chemotaxis, is central to many physiologic events such as axon guidance, wound healing, and tissue morphogenesis. Inappropriate chemotaxis is a key feature of many human diseases, including tumor metastasis, asthma, arthritis, and atherosclerosis. Understanding the mechanisms of chemotaxis is therefore vital for understanding these chemotaxis-related diseases. The long- term goal of our research is to reveal how cells sense their chemical environment and control their migratory behaviors. Using Dictyostelium amoebae as our discovery tool and human cells as our translational tool, we focus on the potent intracellular signal phosphatidylinositol-3,4,5-triphosphate (PIP3), which is produced at the leading edge of cells and reorganizes the actin cytoskeleton. An important, but unanswered, question in the field of chemotaxis is how cells stably maintain the signaling network and remodel the actin cytoskeleton in chemoattractant gradients. To address this fundamental problem, our current studies identified: i) a signaling step that stabilizes directional sensing by persistently orientig Ras activation and PIP3 production, ii) a molecular link that directly binds to both PIP3 and the actin cytoskeleton, and iii) a conserved process in Dictyostelium and humans that turns off PIP3 signaling through translocation of the PIP3 phosphatase PTEN to the plasma membrane. In the next funding period, we propose to study each of these regulatory events and the mechanisms by which chemotactic signaling controls cell migration with high precision. In Aim 1, we will determine how directional sensing is spatially directed toward chemoattractants. We hypothesize that the activation of Ras GTPases and PIP3 production that occurs at the leading portion of cells is regulated by active Rho GTPases located at the rear end through chemical gradients. We will examine how Rho GTPases transmit signal to Ras GTPases. In Aim 2, we will determine how PIP3-binding monomeric myosin I converts the PIP3 signal to the actin cytoskeleton. We will test three models for the function of myosin I in cytoskeletal remodeling: connecting actin filaments to the plasma membrane, directly polymerizing actin, and recruiting actin nucleation factors. In Aim 3, we will delineate how human PTEN is recruited to the plasma membrane. We hypothesize that previously unidentified PTEN receptors in the plasma membrane mediate this process in human cells. We will examine the function of newly identified human PTEN-binding proteins in the localization of PTEN. Moreover, we will further determine the functional importance of the receptors in PIP3 signaling. The outcomes of our research are expected to provide a conceptual breakthrough into two central events in chemotaxis, directional sensing and cytoskeletal rearrangements, and may lead to development of chemotaxis-based treatments for cancer and inflammation.