Ahmed Tasneem, Shea Kerry, Masters John R W, Jones Gareth E, Wells Claire M
Randall Division of Cell and Molecular Biophysics, King's College London, UK.
Cell Signal. 2008 Jul;20(7):1320-8. doi: 10.1016/j.cellsig.2008.02.021. Epub 2008 Mar 12.
Hepatocyte growth factor (HGF) is associated with tumour progression and increases the invasiveness of prostate carcinoma cells. Cell migration and invasion requires reorganisation of the actin cytoskeleton; processes mediated by the Rho family GTPases. p21 activated kinase 4 (PAK4), an effector of the Rho family protein Cdc42, is activated downstream of HGF. We report here the novel finding that in prostate cancer cells PAK4 binds to and phosphorylates LIM kinase 1 (LIMK1) in an HGF-dependent manner. We show for the first time that variations in the level of PAK4 expression change the level of cofilin phosphorylation in cells, a change we correlate with LIMK1 activity, cell morphology and migratory behaviour. We identify for the first time a direct and localised interaction between PAK4 and LIMK1 within cells using FRET: FLIM. Moreover we show here that HGF mediates this interaction which is concentrated in small foci at the cell periphery. PAK4 and LIMK1 act synergistically to increase cell migration speed, whilst a reduction in PAK4 expression decreases cell speed. It is well established that unphosphorylated (active) cofilin is a required to drive cell migration. Our results support a model whereby HGF-stimulated cell migration also requires a cofilin phosphorylation step that is mediated by PAK4.
肝细胞生长因子（HGF）与肿瘤进展相关，并增加前列腺癌细胞的侵袭性。细胞迁移和侵袭需要肌动蛋白细胞骨架的重组，这一过程由Rho家族GTP酶介导。p21活化激酶4（PAK4）是Rho家族蛋白Cdc42的效应器，在HGF下游被激活。我们在此报告一项新发现，即在前列腺癌细胞中，PAK4以HGF依赖的方式与LIM激酶1（LIMK1）结合并使其磷酸化。我们首次表明，PAK4表达水平的变化会改变细胞中丝切蛋白的磷酸化水平，这种变化与LIMK1活性、细胞形态和迁移行为相关。我们首次使用荧光共振能量转移：荧光寿命成像（FRET: FLIM）在细胞内鉴定出PAK4与LIMK1之间直接且局部的相互作用。此外，我们在此表明HGF介导这种相互作用，其集中在细胞周边的小焦点处。PAK4和LIMK1协同作用以提高细胞迁移速度，而PAK4表达的降低会降低细胞速度。众所周知，未磷酸化（活性）的丝切蛋白是驱动细胞迁移所必需的。我们的结果支持一种模型，即HGF刺激的细胞迁移也需要由PAK4介导的丝切蛋白磷酸化步骤。
