Molecular Elucidation of Integrin Signaling

描述（由申请人提供）：我们的提案的广泛的长期目标是获得细胞粘附的详细分子理解，并阐明它如何介导各种生理和病理过程。在过去的资助期间，我们一直专注于研究整合素的机制，整合素是一类异二聚体（α/β）跨膜受体，在细胞粘附，特别是细胞-ECM粘附中发挥关键作用。通过进行强有力的结构研究，我们和其他人已经取得了重大进展，对整合素是如何激活触发细胞-ECM粘附的分子理解。在本延续研究提案中，我们希望开始研究整合素激活后的事件，即，由外向内信号传导，其中整联蛋白胞外结构域粘附于ECM，并将信号传导至细胞质面，从而触发连接至细胞骨架的细胞内信号传导途径的级联。广泛的遗传学和生物化学研究表明，这种由外向内的信号传导过程对于调节动态粘附事件如细胞形状变化（扩散）、细胞迁移、增殖和存活是必不可少的，但其潜在机制仍然知之甚少。作为我们研究的第一步，我们将通过解决以下直接问题来关注一些关键但代表性的途径：（i）在整合素活化及其随后的ECM接合后，小整合素α/β胞质尾（CT，大多数为20-50个残基）如何准确地识别导致不同细胞内事件的不同效应物？(ii)这些不同的整合素-效应物相互作用是如何被调节以介导动态细胞粘附事件的？在初步研究中，我们已经发现，虽然整合素效应物特异性地与各种整合素CT相互作用，但这些相互作用与其相应的下游相互作用令人惊讶地相互排斥。这使我们假设一种反馈机制，通过其下游靶点调节整合素-效应物相互作用的开/关开关。这种反馈调节可以促进周期性细胞铺展和迁移过程中整合素-细胞骨架的有效组装/重组。因此，我们的目标是2倍：（a）定义这些相互作用的分子特异性;（B）大力评估假设的反馈机制。我们将继续采用结构和职能相结合的办法来实现我们的目标。我们相信，这些结果不仅将为不同的整合素-效应物相互作用如何介导不同的由外而内的信号通路提供关键的分子见解，而且还将解开一个统一的邮政编码，即，反馈控制，用于指导高度协调和动态的小区扩展和迁移过程。由于参与这些途径的成分的功能障碍与许多人类疾病相关，因此这里得出的具体结果也可能具有治疗价值。

DESCRIPTION (provided by applicant): The broad long-range objective of our proposal is to obtain a detailed molecular understanding of cell adhesion and to elucidate how it mediates various physiological and pathological processes. Over the past funding period, we have been focusing on studying the mechanism of integrins, a class of heterodimeric (alpha/beta) transmembrane receptors that play key roles in the cell adhesion, particularly the cell-ECM adhesion. By performing vigorous structural studies, we and others have made a major progress toward the molecular understanding of how integrins are activated to trigger the cell-ECM adhesion. In this continuation proposal, we wish to begin the investigation on the events following the integrin activation, i.e., outside-in signaling where integrin extracellular domain adheres to ECM and elicits signals to the cytoplasmic face triggering cascades of intracellular signaling pathways that link to cytoskeleton. Extensive genetic and biochemical studies have shown that such outside-in signaling process is essential for regulating dynamic adhesion events such as cell shape change (spreading), cell migration, proliferation, and survival, yet the underlying mechanism remains poorly understood. As a first step of our investigation, we will focus on some critical yet representative pathways by addressing the following immediate questions: (i) Upon integrin activation and its subsequent ECM engagement, how exactly do the small integrin alpha/beta cytoplasmic tails (CTs, mostly 20-50 residues) recognize different effectors leading to different intracellular events? (ii) how are these different integrin-effector interactions modulated to mediate the dynamic cell adhesion events? In preliminary studies, we have found that while integrin effectors specifically interact with various integrin CTs, these interactions are surprisingly mutually exclusive with their corresponding downstream ones. This has led us to hypothesize a feedback mechanism for regulating the on/off switch of the integrin-effector interactions by their downstream targets. Such feedback regulation may promote efficient integrin-cytoskeleton assembly/reassembly during the cyclic cell spreading and migration processes. Hence our goals are 2 fold: (a) to define the molecular specificity of these interactions; and (b) to vigorously evaluate the hypothesized feedback mechanism. We will continue to use the combined structural and functional approach to pursue our goals. We believe that the results will not only provide key molecular insights into how different integrin-effector interactions mediate distinct outside-in signaling pathways but also unravel a unifying zip code, i.e., the feedback control, for directing the highly coordinated and dynamic cell spreading and migration processes. Since dysfunctions of components involved in these pathways are correlated with numerous human disorders, the specific results derived here may be also of therapeutic value.