Webb Bradley A, Eves Robert, Crawley Scott W, Zhou Shutang, Côté Graham P, Mak Alan S
Department of Biochemistry and Protein Function Discovery Program, Queen's University, Botterell Hall, Room 616, Kingston, Ontario, Canada K7L 3N6.
Am J Physiol Cell Physiol. 2005 Oct;289(4):C898-907. doi: 10.1152/ajpcell.00095.2005. Epub 2005 Jun 8.
Remodeling of the vascular smooth muscle cytoskeleton is essential for cell motility involved in the development of diseases such as arteriosclerosis and restenosis. The p21-activated kinase (PAK), which is an effector of the Rho GTPases Rac and Cdc42, has been shown to be involved in cytoskeletal remodeling and cell motility. We show herein that expression of cytoskeletally active constructs of PAK1 is able to induce the formation of dynamic, podosome-like F-actin columns in the A7r5 vascular smooth muscle cell line. Most of these actin columns appear at the junctions between stress fibers and focal adhesions and contain several known podosomal protein markers, such as cortactin, Arp2/3, alpha-actinin, and vinculin. The kinase activity of PAK plays a role in the regulation of the turnover rates of these actin columns but is not essential for their formation. The ability of PAK to interact with the PAK-interacting exchange factor (PIX) but not with Rac or Cdc42, however, is required for the formation of the actin columns as well as for the translocation of PIX and G protein-coupled receptor kinase-interacting protein (GIT) to focal adhesions adjacent to the actin columns. These findings suggest that interaction between PAK and PIX, as well as the recruitment of PIX and GIT to focal adhesions, plays an important role in the formation of actin columns that resemble podosomes induced by phorbol ester in vascular smooth muscle cells.
血管平滑肌细胞骨架的重塑对于参与诸如动脉硬化和再狭窄等疾病发展过程中的细胞运动至关重要。p21激活激酶（PAK）作为Rho GTPases家族成员Rac和Cdc42的效应器，已被证明参与细胞骨架重塑和细胞运动。我们在此表明，PAK1细胞骨架活性构建体的表达能够在A7r5血管平滑肌细胞系中诱导动态的、类似足体的F-肌动蛋白柱的形成。这些肌动蛋白柱大多出现在应力纤维和粘着斑之间的连接处，并包含几种已知的足体蛋白标记物，如皮层肌动蛋白、Arp2/3、α-辅肌动蛋白和纽蛋白。PAK的激酶活性在调节这些肌动蛋白柱的周转率中起作用，但对其形成并非必不可少。然而，PAK与PAK相互作用交换因子（PIX）相互作用的能力，而非与Rac或Cdc42相互作用的能力，对于肌动蛋白柱的形成以及PIX和G蛋白偶联受体激酶相互作用蛋白（GIT）向肌动蛋白柱相邻的粘着斑的转位是必需的。这些发现表明，PAK与PIX之间的相互作用，以及PIX和GIT向粘着斑的募集，在血管平滑肌细胞中由佛波酯诱导的类似足体的肌动蛋白柱的形成中起重要作用。
