Regulation of a lipid raft trafficking pathway by integrins

描述（由申请人提供）：整合素介导的粘附控制生长因子和细胞因子受体下游许多信号的传递。这些作用调节细胞生长、分化和许多其他功能。我们以前的工作确定了一个整合素调节的膜运输途径，介导了一些这些影响。锚定依赖性细胞从其细胞外基质中脱离，触发脂筏成分通过小窝内化.这些结构域从质膜上的清除抑制了Rho家族GTP酶、Erk和Akt的生长因子活化。将细胞重新接种在细胞外基质上触发这些组分的胞吐作用，以促进细胞铺展和恢复信号传导。在上一个资助期间，我们确定Arf 6是胞吐作用第一步的关键决定因素：筏组分从再循环内体中退出。然后，我们表明，RalA介导的下一步，对接在质膜上的胞吐囊泡通过其与外囊的相互作用。RalA在许多系统中被认为是生长和癌症转移的锚定依赖性的特异性调节剂，因此，我们的数据将整合素对膜运输的调节与肿瘤生长和转移联系起来。我们现在建议研究整合素控制胞吐途径的机制，并研究其在细胞运动中的作用。具体而言，我们将阐明整合素调节RalA在脂筏胞吐的机制，通过确定相关的鸟嘌呤核苷酸交换因子介导的整合素激活RalA，并进一步确定激活的机制。我们将同样确定介导Arf6激活的交换因子并研究其机制。最后，我们将阐明整合素调节的脂筏运输在细胞运动中的作用，特别是是否有空间限制的调节脂筏贩运通过相同的途径，以及它如何有助于定向细胞运动。这项工作将有助于我们理解一个对细胞行为至关重要的途径，以及调节癌症转移的关键。 公共卫生相关性：整合素信号传导是控制细胞生长、迁移、组织形成和形态发生的基本细胞调节机制之一。这些途径中的缺陷导致免疫缺陷、自身免疫性疾病、出生缺陷和癌症，仅举几例。整合素信号传导介导细胞生长的锚定依赖性，这是一种防止癌症转移的基本机制。本项目旨在阐明整合素调节脂筏囊泡转运的途径及其对细胞迁移和信号传导的影响。我们以前对这一通路的研究表明，它受到与癌症转移高度相关的基因产物的调控。因此，该项目与理解和潜在治疗癌症转移直接相关，并对人类广泛的形态发生和迁移过程产生重要影响。

DESCRIPTION (provided by applicant): Integrin-mediated adhesion controls the transmission of many signals downstream of growth factor and cytokine receptors. These effects modulate cell growth, differentiation and many other functions. Our previous work identified an integrin-regulated membrane trafficking pathway that mediates a number of these effects. Detachment of anchorage- dependent cells from their extracellular matrix triggers internalization of lipid raft components via caveolae. The resultant clearance of these domains from the plasma membrane inhibits growth factor activation of Rho family GTPases, Erk and Akt. Replating cells on extracellular matrix triggers exocytosis of these components to promote cell spreading and restore signaling. During the last grant period, we identified Arf6 as the key determinant of the first step of exocytosis: exit of raft components from the recycling endosomes. We then showed that RalA mediates the next step, docking of exocytic vesicles at the plasma membrane through its interaction with the exocyst. RalA has been implicated as a specific regulator of anchorage-dependence of growth and cancer metastasis in many systems, thus, our data link integrin regulation of membrane trafficking with tumor growth and metastasis. We now propose to investigate the mechanisms by which integrins control the exocytosis pathway and investigate its role in cell motility. Specifically, we will elucidate the mechanism by which integrins regulate RalA during lipid raft exocytosis by identifying the relevant guanine nucleotide exchange factor that mediates integrin activation of RalA and further define the mechanism of activation. We will similarly identify the exchange factors that mediate Arf6 activation and investigate mechanism. Lastly, we will elucidate the role of integrin-regulated lipid raft transport in cell motility, specifically whether there is spatially restricted regulation of lipid raft trafficking via the same pathway and how it contributes to directed cell movement. This work will contribute to our understanding of a pathway that is fundamental to cell behavior as well as crucial in regulating cancer metastasis. PUBLIC HEALTH RELEVANCE: Integrin signaling is one of the basic cellular regulatory mechanisms that governs cell growth, migration, tissue organization and morphogenesis. Defects in these pathways lead to immune deficiencies, autoimmune diseases, birth defects and cancer to name but a few. Integrin signaling mediates anchorage dependence of cell growth, a fundamental mechanism that serves as a safeguard against cancer metastasis. This project aims to elucidate the pathways by which integrins regulate lipid raft vesicular transport and subsequent effects on cell migration and signaling. Our previous work on this pathway has shown that it is regulated by gene products that are highly linked to cancer metastasis. This project therefore has direct relevance for understanding and potentially treating cancer metastasis, as well as important implications for a wide range of morphogenetic and migratory processes in humans.