The role of toca-1-N-wasp complex in filopodia formation and endocytosis

Abstract

Transducer of Cdc42 mediated actin polymerization (Toca-1) was identified in 2004 as an essential component of Cdc42 mediated actin polymerization using Xenopus extract. Toca-1 consists of an F-BAR domain at the N-terminal, an HR1 domain (Cdc42 binding site) in the middle and an SH3 domain (N-WASP binding site) at the C-terminal. N-WASP is an activator of actin nucleation through the Arp2/3 complex. Toca-1 or N-WASP induces neurite outgrowth and filopodia formation in N1E115 cells. Toca-1 requires the F-BAR domain, Cdc42 binding site and SH3 domain to induce filopodia. Toca-1 and N-WASP require each other for filopodia formation and synergize to induce filopodia. Toca-1 does not localize in filopodia but is recruited to filopodia by N-WASP. Toca-1 directly interacts with N-WASP in filopodia and Rab5 positive vesicles. Coexpression of Toca-1 and N-WASP affects the distribution and size of Rab5 positive vesicles. Therefore this Toca-1-N-WASP complex not only localizes in filopodia but also induces the formation of filopodia and endocytic vesicles. Three inhibitors of endocytosis, dynamin-K44A, Eps15Δ95/295, and clathrin heavy chain RNAi, block Toca-1 induced filopodia formation. These data suggest that the Toca-1-N-WASP complex can link filopodia formation to endocytosis. The coordinated filopodia formation and endocytosis may be crucial for diverse cellular and developmental processes, such as growth cone guidance and collapse, epithelial cell polarity and border cell migration of Drosophila. Therefore the linkage between filopodia formation and endocytosis may be essential for cellular response to the environmental cues or establishing cell polarity, thus providing a mechanism to coordinate cell signaling events and developmental processes.