Morita Tsuyoshi, Mayanagi Taira, Yoshio Toshiyuki, Sobue Kenji
Department of Neuroscience (D13), Osaka University Graduate School of Medicine, Yamadaoka 2-2, Suita, Osaka 565-0871, Japan.
J Biol Chem. 2007 Mar 16;282(11):8454-63. doi: 10.1074/jbc.M609983200. Epub 2007 Jan 15.
Podosomes are dynamic cell adhesion structures that degrade the extracellular matrix, permitting extracellular matrix remodeling. Accumulating evidence suggests that actin and its associated proteins play a crucial role in podosome dynamics. Caldesmon is localized to the podosomes, and its expression is down-regulated in transformed and cancer cells. Here we studied the regulatory mode of caldesmon in podosome formation in Rous sarcoma virus-transformed fibroblasts. Exogenous expression analyses revealed that caldesmon represses podosome formation triggered by the N-WASP-Arp2/3 pathway. Conversely, depletion of caldesmon by RNA interference induces numerous small-sized podosomes with high dynamics. Caldesmon competes with the Arp2/3 complex for actin binding and thereby inhibits podosome formation. p21-activated kinases (PAK)1 and 2 are also repressors of podosome formation via phosphorylation of caldesmon. Consequently, phosphorylation of caldesmon by PAK1/2 enhances this regulatory mode of caldesmon. Taken together, we conclude that in Rous sarcoma virus-transformed cells, changes in the balance between PAK1/2-regulated caldesmon and the Arp2/3 complex govern the formation of podosomes.
足体是一种动态的细胞黏附结构，可降解细胞外基质，从而实现细胞外基质重塑。越来越多的证据表明，肌动蛋白及其相关蛋白在足体动态变化中起关键作用。钙调蛋白定位于足体，其表达在转化细胞和癌细胞中下调。在此，我们研究了钙调蛋白在劳氏肉瘤病毒转化的成纤维细胞足体形成中的调控模式。外源表达分析表明，钙调蛋白可抑制由N-WASP-Arp2/3途径触发的足体形成。相反，通过RNA干扰耗尽钙调蛋白会诱导大量具有高动态性的小型足体。钙调蛋白与Arp2/3复合物竞争肌动蛋白结合，从而抑制足体形成。p21激活激酶（PAK）1和2也是通过钙调蛋白磷酸化来抑制足体形成的。因此，PAK1/2介导的钙调蛋白磷酸化增强了钙调蛋白的这种调控模式。综上所述，我们得出结论，在劳氏肉瘤病毒转化的细胞中，PAK1/2调控的钙调蛋白与Arp2/3复合物之间平衡的变化决定了足体的形成。
