Critchley D R, Holt M R, Barry S T, Priddle H, Hemmings L, Norman J
Department of Biochemistry, University of Leicester, U.K.
Biochem Soc Symp. 1999;65:79-99.
Members of the integrin family of cell adhesion molecules play a pivotal role in the interaction between animal cells and the extracellular matrix. This article reviews the evidence (i) that the integrin beta-subunit cytoplasmic domain is important in the localization of integrins to focal adhesions, and for integrin-mediated cell adhesion/spreading; and (ii) that the integrin beta-subunit can be linked to F-actin via the actin-binding proteins talin, alpha-actinin and filamin. Talin has two or more actin-binding sites, and three binding sites for the cytoskeletal protein vinculin. Because vinculin can also bind F-actin, it may cross-link talin and actin, thereby stabilizing the interaction. In addition, vinculin contains a binding site for VASP (vasodilator-stimulated phospho-protein), a protein which may serve to recruit a profilin/G-actin complex to talin, which has actin-nucleating activity. Evidence that talin, vinculin and alpha-actinin are important in the assembly of focal adhesions, obtained using antisense technology and protein microinjection, is reviewed. To analyse the role of talin in focal adhesions, we have disrupted both copies of the talin gene in mouse embryonic stem (ES) cells. Undifferentiated talin (-/-) ES cell mutants are unable to assemble focal adhesions when plated on fibronectin, whereas vinculin (-/-) ES cells are able to do so. Finally, the role of small GTP-binding proteins in the assembly of focal adhesions is discussed, along with our recent studies using streptolysin-O-permeabilized Swiss 3T3 cells which suggest that the GTP-binding protein ADP-ribosylation factor-1 (ARF-1) is important in targeting the protein paxillin to focal adhesions.
细胞黏附分子整合素家族的成员在动物细胞与细胞外基质之间的相互作用中起着关键作用。本文综述了以下证据：（i）整合素β亚基胞质结构域对于整合素定位于黏着斑以及整合素介导的细胞黏附/铺展很重要；（ii）整合素β亚基可通过肌动蛋白结合蛋白踝蛋白、α-辅肌动蛋白和细丝蛋白与F-肌动蛋白相连。踝蛋白有两个或更多个肌动蛋白结合位点，以及三个与细胞骨架蛋白纽蛋白结合的位点。由于纽蛋白也能结合F-肌动蛋白，它可能会交联踝蛋白和肌动蛋白，从而稳定这种相互作用。此外，纽蛋白含有一个与血管扩张刺激磷蛋白（VASP）结合的位点，VASP可能会将一个肌动蛋白单体结合蛋白/球形肌动蛋白复合物招募到具有肌动蛋白成核活性的踝蛋白处。本文还综述了利用反义技术和蛋白质显微注射获得的关于踝蛋白、纽蛋白和α-辅肌动蛋白在黏着斑组装中很重要的证据。为了分析踝蛋白在黏着斑中的作用，我们破坏了小鼠胚胎干细胞（ES细胞）中的两个踝蛋白基因拷贝。未分化的踝蛋白缺失（-/-）ES细胞突变体在铺在纤连蛋白上时无法组装黏着斑，而纽蛋白缺失（-/-）ES细胞则能够做到。最后，本文讨论了小GTP结合蛋白在黏着斑组装中的作用，以及我们最近使用链球菌溶血素O通透的瑞士3T3细胞进行的研究，这些研究表明GTP结合蛋白ADP核糖基化因子1（ARF-1）在将桩蛋白靶向黏着斑方面很重要。
