Transient Activations of Rac1 at the Lamellipodium Tip Trigger Membrane Protrusion.
Current Biology. 2019-09-01; 29(17): 2852-2866.e5
Lire sur PubMed
Mehidi A(1), Rossier O(1), Schaks M(2), Chazeau A(1), Binamé F(3), Remorino A(4), Coppey M(4), Karatas Z(1), Sibarita JB(1), Rottner K(2), Moreau V(3), Giannone G(5).
(1)Interdisciplinary Institute for Neuroscience, Université de Bordeaux, UMR 5297, 33000 Bordeaux, France; Interdisciplinary Institute for Neuroscience, CNRS, UMR 5297, 33000 Bordeaux, France.
(2)Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany; Department of Cell Biology, Helmholtz Centre for Infection Research, Inhoffenstrasse 7, 38124 Braunschweig, Germany.
(3)INSERM, Université de Bordeaux, UMR1053 Bordeaux Research in Translational Oncology, BaRITOn, 33000 Bordeaux, France.
(4)Laboratoire Physico-Chimie, Institut Curie, CNRS UMR168, Paris-Science Lettres, Université Pierre et Marie Curie-Paris 6, 75005 Paris, France.
(5)Interdisciplinary Institute for Neuroscience, Université de Bordeaux, UMR 5297, 33000 Bordeaux, France; Interdisciplinary Institute for Neuroscience, CNRS, UMR 5297, 33000 Bordeaux, France. Electronic address: .
The spatiotemporal coordination of actin regulators in the lamellipodium determines the dynamics and architecture of branched F-actin networks during cell migration. The WAVE regulatory complex (WRC), an effector of Rac1 during cell protrusion, is concentrated at the lamellipodium tip. Thus, activated Rac1 should operate at this location to activate WRC and trigger membrane protrusion. Yet correlation of Rho GTPase activation with cycles of membrane protrusion previously revealed complex spatiotemporal patterns of Rac1 and RhoA activation in the lamellipodium. Combining single protein tracking (SPT) and super-resolution imaging with loss- or gain-of-function mutants of Rho GTPases, we show that Rac1 immobilizations at the lamellipodium tip correlate with its activation, in contrast to RhoA. Using Rac1 effector loop mutants and wild-type versus mutant variants of WRC, we show that selective immobilizations of activated Rac1 at the lamellipodium tip depend on effector binding, including WRC. In contrast, wild-type Rac1 only displays slower diffusion at the
lamellipodium tip, suggesting transient activations. Local optogenetic activation of Rac1, triggered by membrane recruitment of Tiam1, shows that Rac1 activation must occur close to the lamellipodium tip and not behind the lamellipodium to trigger efficient membrane protrusion. However, coupling tracking with optogenetic activation of Rac1 demonstrates that diffusive properties of wild-type Rac1 are unchanged despite enhanced lamellipodium protrusion. Taken together, our results support a model whereby transient activations of Rac1 occurring close to the lamellipodium tip trigger WRC binding. This short-lived activation ensures a local and rapid control of Rac1 actions on its effectors to trigger actin-based protrusion.
Copyright © 2019 Elsevier Ltd. All rights reserved.