The Cytoskele­ton and Cell Migra­tion

Pro­tein assem­blies are recruited to the tips of lamel­lipo­dia and filopo­dia that reg­u­late and drive the poly­meri­sa­tion of actin for pro­tru­sion. For reviews see Stradal et al., 2004; Chesarone and Goode, 2009; Tak­e­nawa and Suet­sugu, 2007; Derivery and Gautreau, 2010.

Live cell microscopy with GFP-tagged pro­teins has shown that mem­bers of this com­plex are specif­i­cally tar­geted to lamel­lipo­dia at the onset of pro­tru­sion (Hahne et al., 2001; Nak­a­gawa et al., 2003; Rot­tner et al., 1999; Stradal et al., 2001). The fol­low­ing movies show some mem­bers of the tip com­plex in lamel­lipo­dia and filopo­dia: mouse melanoma cells were trans­fected with the pro­teins indi­cated, tagged with GFP:

VASP

Abi-1

Scar WAVE1

Scar WAVE2

IRSp53.

The WAVE com­plex com­prises in mam­mals Scar/WAVE and Abi, Sra1/PIR121, Nap1 (or haematopoi­etic Hem1) and Brick1/HSPC300. The role of WAVE is to acti­vate the Arp2/3 com­plex to ini­ti­ate actin branch­ing for the gen­er­a­tion of actin net­works in lamel­lipo­dia. Actin branch­ing can be repro­duced in vitro by mix­ing actin with an active domain of the WAVE or WASP pro­tein and the Arp2/3 com­plex (Amann and Pol­lard, 2001):

Branch­ing of actin in vitro by WAVE and the Arp2/3 com­plex observed using TIRF microscopy. Cour­tesy of Kai Schlueter and There­sia Stradal (unpub­lished).

As shown by the Welch group, the Arp2/3 com­plex is local­ized over the whole lamel­lipodium net­work. Pho­to­bleach exper­i­ments show that the Aprp2/3 com­plex tread­mills with actin in the lamel­lipodium:

Flu­o­res­cence recov­ery after pho­to­bleach­ing (FRAP) in the lamel­lipodium of a B16 melanoma cell express­ing Actin-RFP and ArpC5-GFP. Note that the recov­ery of the Arp label par­al­lels the recov­ery of actin (Lai et al., 2008). As shown by the Svitk­ina group, the Arp com­plex is absent from the core of actin bun­dles (microspikes) that trans­verse the lamel­lipodium. Video cour­tesy of Mal­go­zata Szco­zo­drak and Kle­mens Rot­tner (unpub­lished).

VASP is a mem­ber of the Ena/VASP fam­ily of pro­teins that act as pro­ces­sive elon­ga­tors of actin fil­a­ments (Bre­it­sprecher et al., 2011), as shown in the two fig­ures below:

Plas­tic beads coated with VASP pro­mote the growth of actin fil­a­ments at the bead sur­face by teth­er­ing actin fil­a­ments and feed­ing monomers into the plus ends. From Bre­it­sprecher et al., 2008.

Shows again the local­iza­tion of VASP at pro­trud­ing lamel­lipo­dia and filopo­dia tips in a fish fibrob­last express­ing VASP-GFP and Actin-RFP.

Schematic illus­tra­tion of some of the pro­teins and pro­tein com­plexes engaged in ini­ti­at­ing and organ­is­ing lamel­lipo­dia and filopo­dia. (Small et al., 2002)

Related Pub­li­ca­tions

• Amann, K.J., Pol­lard T.D. (2001). The Arp2/3 com­plex nucle­ates actin fil­a­ment branches from the sides of pre-existing fil­a­ments. Nat Cell Biol. 3:306–10.
• Bre­it­sprecher, D., Kiesewet­ter, A.K., Linkner, J., Urbanke, C., Resch, G.P., Small, J.V., Faix, J. (2008). Clus­ter­ing of VASP actively dri­ves pro­ces­sive, WH2 domain-mediated actin fil­a­ment elon­ga­tion. EMBO J. 2008 27(22): 2943 — 2954.
• Bre­it­sprecher, D., Kiesewet­ter, A.K., Linkner, J., Vinzenz, M., Stradal, T.E., Small, J.V., Curth, U., Dick­in­son, R.B., Faix J. (2011). Mol­e­c­u­lar mech­a­nism of Ena/VASP-mediated actin-filament elon­ga­tion. EMBO J. 30:456–67.
• Chesarone, M., A., Goode, B., L. (2009). Actin nucle­ation and elon­ga­tion fac­tors: mech­a­nisms and inter­play. Curr. Opin. Cell. Biol. 21, 28–37.
• Derivery, E. and Gautreau, A. (2010).  Gen­er­a­tion of branched actin net­works: assem­bly and reg­u­la­tion of the N-WASP and WAVE mol­e­c­u­lar machines. Bioes­says. 32, 119–131.
• Hahne, P., Sechi, A., Benesch, S. and Small, J.V. (2001). Scar/WAVE is localised at the tips of pro­trud­ing lamel­lipo­dia in liv­ing cells. FEBS Lett. 492, 215–220.
• Lai, F.P.L., Szc­zo­drak, M., Block, J., Mannherz, H.G., Small, J.V., Stradal, T.E.B., Dunn, G.A. and Rot­tner G.A.K. (2008). Arp2/​3 com­plex inter­ac­tions and actin net­work turnover in lamel­lipo­dia. EMBO J. 27, 982 – 992.
• Nak­a­gawa, H., Miki, H. Nozumi, M. Tak­e­nawa, T. Miyamoto, S. Wehland, J. and Small, J.V. (2003). IRSp53 is co-localised with WAVE2 at the tips of pro­trud­ing lamel­lipo­dia and filopo­dia inde­pen­dently of Mena. J Cell Sci. 116, 2577–83.
• Rot­tner, K., Behrendt, B., Small, JV, Wehland, J. (1999). VASP dynam­ics dur­ing lamel­lipo­dia pro­tru­sion. Nat. Cell. Biol. 1, 321–322.
• Small, JV., Stradal, T., Vig­nal, E. and Rot­tner, K. (2002). The lamel­lipodium: where motil­ity begins. Trends Cell Biol., 12, 112–120.
• Stradal, T., Court­ney, K.D., Rot­tner, K., Hahne, P., Small, J.V. and Pen­der­gast, A.M. (2001). The Abl-interactor (Abi) pro­teins local­ize to sites of actin poly­mer­iza­tion at the tips of lamel­lipo­dia and filopo­dia. Curr. Biol. 11, 891–895.
• Stradal, T. E., Rot­tner, K., Dis­anza, A., Con­falonieri, S., Inno­centi, M., Scita, G. (2004). Reg­u­la­tion of actin dynam­ics by WASP and WAVE fam­ily pro­teins. Trends Cell. Biol. 14, 303–311.
• Tak­e­nawa, T., Suet­sugu, S. (2007). The WASP-WAVE pro­tein net­work: con­nect­ing the mem­brane to the cytoskele­ton. Nat. Rev. Mol. Cell. Biol. 8, 37–48.