Novel roles of formin mDia2 in lamellipodia and filopodia formation in motile cells.
Actin polymerization-driven protrusion of the leading edge is a key element of cell motility. The important actin nucleators formins and the Arp2/3 complex are believed to have nonoverlapping functions in inducing actin filament bundles in filopodia and dendritic networks in lamellipodia, respectively. We tested this idea by investigating the role of mDia2 formin in leading-edge protrusion by loss-of-function and gain-of-function approaches. Unexpectedly, mDia2 depletion by short interfering RNA (siRNA) severely inhibited lamellipodia. Structural analysis of the actin network in the few remaining lamellipodia suggested an mDia2 role in generation of long filaments. Consistently, constitutively active mDia2 (DeltaGBD-mDia2) induced accumulation of long actin filaments in lamellipodia and increased persistence of lamellipodial protrusion. Depletion of mDia2 also inhibited filopodia, whereas expression of DeltaGBD-mDia2 promoted their formation. Correlative light and electron microscopy showed that DeltaGBD-mDia2-induced filopodia were formed from lamellipodial network through gradual convergence of long lamellipodial filaments into bundles. Efficient filopodia induction required mDia2 targeting to the membrane, likely through a scaffolding protein Abi1. Furthermore, mDia2 and Abi1 interacted through the N-terminal regulatory sequences of mDia2 and the SH3-containing Abi1 sequences. We propose that mDia2 plays an important role in formation of lamellipodia by nucleating and/or protecting from capping lamellipodial actin filaments, which subsequently exhibit high tendency to converge into filopodia.
Changsong
C
Yang
Lubov
L
Czech
Silke
S
Gerboth
Shin-ichiro
S
Kojima
Giorgio
G
Scita
Tatyana
T
Svitkina
D051376:Actin-Related Protein 2-3 Complex / Q000235:genetics / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement / Q000502:physiology*; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D000080865:Formins; D015870:Gene Expression; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008855:Microscopy, Electron, Scanning; D011554:Pseudopodia / Q000378:metabolism* / Q000648:ultrastructure; D034741:RNA, Small Interfering / Q000235:genetics
C513733:ABI1 protein, human; C513734:Abi1 protein, mouse; D051376:Actin-Related Protein 2-3 Complex; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; C491462:DIAPH2 protein, human; C491463:Diap2 protein, mouse; D000080865:Formins; D034741:RNA, Small Interfering