Zegers Mirjam M P, Forget Marie-Annick, Chernoff Jonathan, Mostov Keith E, ter Beest Martin B A, Hansen Steen H
Department of Anatomy and Biochemistry and Biophysics, University of California San Francisco, Box 2140, 600 16th Street, San Francisco, CA 94143, USA.
EMBO J. 2003 Aug 15;22(16):4155-65. doi: 10.1093/emboj/cdg398.
Wound healing in epithelia requires coordinated cell migration and proliferation regulated by signaling mechanisms that are poorly understood. Here we show that epithelial cells expressing constitutively active or kinase-dead mutants of the Rac/Cdc42 effector Pak1 fail to undergo growth arrest upon wound closure. Strikingly, this phenotype is only observed when the Pak1 kinase mutants are expressed in cells possessing a free lateral surface, i.e. one that is not engaged in contact with neighboring cells. The Pak1 kinase mutants perturb contact inhibition by a mechanism that depends on the Pak-interacting Rac-GEF PIX. In control cells, endogenous activated Pak and PIX translocate from focal complexes to cell-cell contacts during wound closure. This process is abrogated in cells expressing Pak1 kinase mutants. In contrast, Pak1 mutants rendered defective in PIX binding do not impede translocation of activated Pak and PIX, and exhibit normal wound healing. Thus, recruitment of activated Pak and PIX to cell-cell contacts is pivotal to transduction of growth-inhibitory signals from neighboring cells in epithelial wound healing.
上皮组织中的伤口愈合需要协调细胞迁移和增殖，其受信号传导机制调控，但目前对该机制了解甚少。在此我们表明，表达Rac/Cdc42效应蛋白Pak1组成型活性或激酶失活突变体的上皮细胞在伤口闭合时无法经历生长停滞。令人惊讶的是，只有当Pak1激酶突变体在具有自由侧面（即未与相邻细胞接触的侧面）的细胞中表达时，才会观察到这种表型。Pak1激酶突变体通过一种依赖于与Pak相互作用的Rac-GEF PIX的机制扰乱接触抑制。在对照细胞中，内源性活化的Pak和PIX在伤口闭合期间从粘着斑复合体转位至细胞-细胞接触部位。在表达Pak1激酶突变体的细胞中，这一过程被消除。相反，在PIX结合方面存在缺陷的Pak1突变体不会阻碍活化的Pak和PIX的转位，并且表现出正常的伤口愈合。因此，将活化的Pak和PIX募集至细胞-细胞接触部位对于上皮伤口愈合中来自相邻细胞的生长抑制信号的转导至关重要。
