Role of fascin in filopodial protrusion

Abstract

In this study, the mechanisms of actin-bundling in filopodia were examined. Analysis of cellular localization of known actin cross-linking proteins in mouse melanoma B16F1 cells revealed that fascin was specifically localized along the entire length of all filopodia, whereas other actin cross-linkers were not. RNA interference of fascin reduced the number of filopodia, and remaining filopodia had abnormal morphology with wavy and loosely bundled actin organization. Dephosphorylation of serine 39 likely determined cellular filopodia frequency. The constitutively active fascin mutant S39A increased the number and length of filopodia, whereas the inactive fascin mutant S39E reduced filopodia frequency. Fluorescence recovery after photobleaching of GFP-tagged wild-type and S39A fascin showed that dephosphorylated fascin underwent rapid cycles of association to and dissociation from actin filaments in filopodia, with t 1/2 < 10 s. We propose that fascin is a key specific actin cross-linker, providing stiffness for filopodial bundles, and that its dynamic behavior allows for efficient coordination between elongation and bundling of filopodial actin filaments.

EMT, the cytoskeleton, and cancer cell invasion

“…Stabilized by active Wnt signaling or by mutations in the β-catenin phosphorylation/degradation pathway, β-catenin accumulates in the cytoplasm and enters the nucleus where it interacts with members of the Tcf/Lef family of transcription factors and modulates expression of a large number of genes involved in cell proliferation, migration, invasion, and morphogenesis, including cyclin D1, the cell adhesion molecule L1-CAM, matrix metalloproteases (MMP) and the metastasis gene S100A4 [68,69]. Another recently discovered target of β-catenin/Tcf signaling is Fascin, a actin-bundling protein which is essential for filopodia formation and cancer cell invasion [70,71].…”

Targeted inhibition of fascin function blocks tumour invasion and metastatic colonization

“…Fascin is the primary actin cross-linker in filopodia and has no amino-acid sequence homology with other actin-binding proteins [20][21][22][23][24][25] . It has a molecular mass of B55 kDa, functions as a monomer and is required to maximally cross-link the actin filaments into straight, compact and rigid bundles, to impart distinct mechanical stiffness to actin bundles 26,27 .…”

Dual Actin-bundling and Protein Kinase C-binding Activities of Fascin Regulate Carcinoma Cell Migration Downstream of Rac and Contribute to Metastasis

“…In vitro, fascin cross-links filamentous actin (Factin) into tightly packed, parallel bundles in cooperation with Arp2/3 complex and Wiskott-Aldrich syndrome protein Haviv et al, 2006). In intact cells, fascin-and-actin bundles support cortical cell protrusions and growth cone filopodia Adams et al, 1999;Cohan et al, 2001, Adams andAnilkumar et al, 2003;Svitkina et al, 2003;Vignjevic et al, 2006). Fascin contains N-and C-terminal actin-binding sites and the actin cross-linking activity of fascin is negatively regulated by a protein kinase C (PKC) phosphorylation site (serine-39 in human fascin) that lies within the amino-terminal actin-binding site (Ono et al, 1997).…”