Fascin is an actin-bundling protein involved in filopodia assembly and cancer 
invasion and metastasis of multiple epithelial cancer types. Fascin forms stable 
actin bundles with slow dissociation kinetics in vitro and is regulated by 
phosphorylation of serine 39 by protein kinase C (PKC). Cancer cells use 
invasive finger-like protrusions termed invadopodia to invade into and degrade 
extracellular matrix. Invadopodia have highly dynamic actin that is assembled by 
both Arp2/3 complex and formins; they also contain components of membrane 
trafficking machinery such as dynamin and cortactin and have been compared with 
focal adhesions and podosomes. We show that fascin is an integral component of 
invadopodia and that it is important for the stability of actin in invadopodia. 
The phosphorylation state of fascin at S39, a PKC site, contributes to its 
regulation at invadopodia. We further implicate fascin in invasive migration 
into collagen I-Matrigel gels and particularly in cell types that use an 
elongated mesenchymal type of motility in 3D. We provide a potential molecular 
mechanism for how fascin increases the invasiveness of cancer cells, and we 
compare invadopodia with invasive filopod-like structures in 3D.