Efficiency of lamellipodia protrusion is determined by the extent of cytosolic actin assembly.
Cell migration and cell-cell communication involve the protrusion of actin-rich cell surface projections such as lamellipodia and filopodia. Lamellipodia are networks of actin filaments generated and turned over by filament branching through the Arp2/3 complex. Inhibition of branching is commonly agreed to eliminate formation and maintenance of lamellipodial actin networks, but the regulation of nucleation or elongation of Arp2/3-independent filament populations within the network by, for example, formins or Ena/VASP family members and its influence on the effectiveness of protrusion have been unclear. Here we analyzed the effects of a set of distinct formin fragments and VASP on site-specific, lamellipodial versus cytosolic actin assembly and resulting consequences on protrusion. Surprisingly, expression of formin variants but not VASP reduced lamellipodial protrusion in B16-F1 cells, albeit to variable extents. The rates of actin network polymerization followed a similar trend. Unexpectedly, the degree of inhibition of both parameters depended on the extent of cytosolic but not lamellipodial actin assembly. Indeed, excess cytosolic actin assembly prevented actin monomer from rapid translocation to and efficient incorporation into lamellipodia. Thus, as opposed to sole regulation by actin polymerases operating at their tips, the protrusion efficiency of lamellipodia is determined by a finely tuned balance between lamellipodial and cytosolic actin assembly.
Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, 38106 Braunschweig, Germany.|Department of Cell Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
Georgi
G
Dimchev
Department of Cell Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
Anika
A
Steffen
Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, 38106 Braunschweig, Germany.|Department of Cell Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
Frieda
F
Kage
Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, 38106 Braunschweig, Germany.|Department of Cell Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
Vanessa
V
Dimchev
Cytoskeleton Dynamics and Motility, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France.
Julien
J
Pernier
Cytoskeleton Dynamics and Motility, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France.
Marie-France
MF
Carlier
Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, 38106 Braunschweig, Germany k.rottner@tu-braunschweig.de.|Department of Cell Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
Klemens
K
Rottner
D008841:Actin Cytoskeleton / Q000378:metabolism; D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000818:Animals; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002465:Cell Movement / Q000502:physiology; D003599:Cytoskeleton / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D011554:Pseudopodia / Q000378:metabolism / Q000502:physiology*; D000098662:Vasodilator-Stimulated Phosphoprotein
D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D015815:Cell Adhesion Molecules; D008840:Microfilament Proteins; D010750:Phosphoproteins; D000098662:Vasodilator-Stimulated Phosphoprotein