Clark Emily S, Whigham Amy S, Yarbrough Wendell G, Weaver Alissa M
Department of Pathology, Vanderbilt University, Nashville, Tennessee 37232, USA.
Cancer Res. 2007 May 1;67(9):4227-35. doi: 10.1158/0008-5472.CAN-06-3928.
Invadopodia are branched actin-rich structures associated with extracellular matrix (ECM) degradation that collectively form the invasive machinery of aggressive cancer cells. Cortactin is a prominent component and a specific marker of invadopodia. Amplification of cortactin is associated with poor prognosis in head and neck squamous cell carcinomas (HNSCC), possibly because of its activity in invadopodia. Although the role of cortactin in invadopodia has been attributed to signaling and actin assembly, it is incompletely understood. We made HNSCC cells deficient in cortactin by RNA interference knockdown methods. In these cortactin knockdown cells, invadopodia were reduced in number and lost their ability to degrade ECM. In the reverse experiment, overexpression of cortactin dramatically increased ECM degradation, far above and beyond the effect on formation of actin/Arp3-positive invadopodia puncta. Secretion of matrix metalloproteinases (MMP) MMP-2 and MMP-9, as well as plasma membrane delivery of MT1-MMP correlated closely with cortactin expression levels. MMP inhibitor treatment of control cells mimicked the cortactin knockdown phenotype, with abolished ECM degradation and fewer invadopodia, suggesting a positive feedback loop in which degradation products from MMP activity promote new invadopodia formation. Collectively, these data suggest that a major role of cortactin in invadopodia is to regulate the secretion of MMPs and point to a novel mechanism coupling dynamic actin assembly to the secretory machinery, producing enhanced ECM degradation and invasiveness. Furthermore, these data provide a possible explanation for the observed association between cortactin overexpression and enhanced invasiveness and poor prognosis in HNSCC patients.
侵袭性伪足是富含肌动蛋白的分支结构，与细胞外基质（ECM）降解相关，共同构成侵袭性癌细胞的侵袭机制。皮层肌动蛋白是侵袭性伪足的主要成分和特异性标志物。皮层肌动蛋白的扩增与头颈部鳞状细胞癌（HNSCC）的不良预后相关，可能是因为其在侵袭性伪足中的活性。尽管皮层肌动蛋白在侵袭性伪足中的作用已归因于信号传导和肌动蛋白组装，但其作用尚未完全明确。我们通过RNA干扰敲低方法使HNSCC细胞中的皮层肌动蛋白缺失。在这些皮层肌动蛋白敲低的细胞中，侵袭性伪足数量减少，丧失了降解ECM的能力。在反向实验中，皮层肌动蛋白的过表达显著增加了ECM降解，远远超过了对肌动蛋白/Arp3阳性侵袭性伪足斑点形成的影响。基质金属蛋白酶（MMP）MMP-2和MMP-9的分泌以及MT1-MMP的质膜递送与皮层肌动蛋白表达水平密切相关。用MMP抑制剂处理对照细胞可模拟皮层肌动蛋白敲低的表型，ECM降解被消除，侵袭性伪足减少，这表明存在一个正反馈回路，其中MMP活性产生的降解产物促进新的侵袭性伪足形成。总的来说，这些数据表明皮层肌动蛋白在侵袭性伪足中的主要作用是调节MMP的分泌，并指出了一种将动态肌动蛋白组装与分泌机制偶联的新机制，从而增强了ECM降解和侵袭性。此外，这些数据为观察到的皮层肌动蛋白过表达与HNSCC患者侵袭性增强和预后不良之间的关联提供了一种可能的解释。
