INTERACTION OF GPIIB-IIIA WITH THE PLATELET CYTOSKELETON

整合素作为细胞黏附受体与细胞外基质和肌动蛋白细胞骨架相互作用，参与多种生物学过程。尽管Talin被认为是整合素和肌动蛋白细丝之间的连接蛋白，但对其介导整合素-talin相互作用的分子机制(S)知之甚少。此外，talin在整合素介导的信号转导事件中的作用还没有明确的定义。这一设想的中心假设是Talin与整合素的胞质结构域的相互作用通过整合素受体在由内向外和由外向内的信号转导中发挥重要作用。以AlphaIIbbeta3作为整合蛋白的原型，我们的目标是：1)进一步鉴定AlphaIIbbeta3胞质区域的talin结合位点。通过对AlphaIIbbeta3的定向突变，我们将评估AlphaIIbbeta3细胞质结构域的膜旁区域的碱性氨基酸残基在焦点黏附和Talin结合中的作用。此外，我们将研究alphaIIbbeta3的激活和配体占有率是否会调节其与talin的结合亲和力。2)将整合素结合位点(S)定位于Talin的N-端头区和C-端尾区。通过化学交联研究、抑制性抗体的表位定位和定点突变，我们将确定Talin中与AlphaIIbbeta3相互作用的关键残基。3)研究Talin修饰对AlphaIIbbeta3-talin相互作用的调节作用。我们将评估“自内向外”的信号过程(即PKC介导的talin的磷酸化和PtdIns(4，5)P2诱导的talin-vinculin复合体的形成)对talin-alphaIIbbeta3相互作用的亲和力调节的影响。4)确定整合素-talin相互作用在整合素介导的“自外向内”信号转导中的功能意义。在携带AlphaIIbbeta3的CHO细胞中过表达talin头域阻止了细胞的扩散和局部黏附。我们将利用异丙硫代-β-半乳糖苷(IPTG)诱导的成纤维细胞表达系统来检测talin头域的表达对alpha5beta1介导的细胞扩散和局部黏附的主要负面影响。利用该系统，我们还将通过pp60src、pp125FAK和MAP激酶研究整合素-细胞骨架相互作用在“自外向内”信号转导中的作用。

It is well established that integrins are involved in diverse biological processes by serving as cell adhesion receptors that interact with both the extracellular matrix and the actin cytoskeleton. Although talin has been implicated to serve as a linkage protein between integrins and actin filaments, little is known about the molecular mechanism(s) mediating integrin-talin interaction. Furthermore, the role of talin in integrin-mediated signaling events has not been clearly defined. The central hypothesis of this proposal is that the interaction of talin with the cytoplasmic domains of integrins plays an important role in inside-out and outside-in signaling through integrin receptors. Using alphaIIbbeta3 as the prototype integrin, we aim: 1) To further characterize the talin binding site in the cytoplasmic domain of alphaIIbbeta3. By targeted mutagenesis of a alphaIIbbeta3, we will evaluate the role of the basic amino acid residues in the juxtamembrane region of the alphaIIbbeta3 cytoplasmic domain in focal adhesion and talin binding. Furthermore, we will examine whether activation and ligand occupancy of alphaIIbbeta3 would modulate its binding affinity to talin. 2) To localize the integrin binding site(s) within the N- terminal head and C-terminal tail domains of talin. By chemical cross-linking studies, epitope mapping of inhibitory antibodies, and site directed mutagenesis, we will determine the critical residues in talin mediating interaction with alphaIIbbeta3. 3) To investigate the effect of talin modifications on the regulation of alphaIIbbeta3-talin interaction. We will evaluate the effect of "inside-out" signaling processes (i. e., PKC- mediated phosphorylation of talin and PtdIns(4,5)P2-induced talin-vinculin complex formation) on affinity modulation of talin-alphaIIbbeta3 interaction. 4) To determine the functional significance of integrin-talin interaction in integrin-mediated "outside-in"signaling. Overexpression of the talin head domain in CHO cells bearing alphaIIbbeta3 blocks cell spreading and focal adhesion. We will utilize an isopropylthio-beta- galactoside (IPTG)-inducible expression system in fibroblasts to examine the dominant negative effect of the expression of the talin head domain on alpha5beta1-mediated cell spreading and focal adhesion. Using this system, we will also investigate the role of integrin-cytoskeleton interaction on "outside-in" signaling through pp60src, pp125FAK and MAP kinase.