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Published online October 22, 2007
doi:10.1083/jcb.200705122
The Journal of Cell Biology, Vol. 179, No. 2, 239-245
The Rockefeller University Press, 0021-9525 $30.00
© 2007 Sun et al.
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 Rac1 and Rac2 differentially regulate actin free barbed end formation downstream of the fMLP receptor

Chun Xiang Sun, Marco A.O. Magalhães, and Michael Glogauer

The Canadian Institutes of Health Research Group in Matrix Dynamics and Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada M5G 1G6

Correspondence to Michael Glogauer: michael.glogauer{at}utoronto.ca

Actin assembly at the leading edge of migrating cells depends on the availability of high-affinity free barbed ends (FBE) that drive actin filament elongation and subsequent membrane protrusion. We investigated the specific mechanisms through which the Rac1 and Rac2 small guanosine triphosphatases (GTPases) generate free barbed ends in neutrophils. Using neutrophils lacking either Rac1 or Rac2 and a neutrophil permeabilization model that maintains receptor signaling to the actin cytoskeleton, we assessed the mechanisms through which these two small GTPases mediate FBE generation downstream of the formyl-methionyl-leucyl-phenylalanine receptor. We demonstrate here that uncapping of existing barbed ends is mediated through Rac1, whereas cofilin- and ARP2/3-mediated FBE generation are regulated through Rac2. This unique combination of experimental tools has allowed us to identify the relative roles of uncapping (15%), cofilin severing (10%), and ARP2/3 de novo nucleation (75%) in FBE generation and the respective roles played by Rac1 and Rac2 in mediating actin dynamics.

C.X. Sun and M.A.O. Magalhães contributed equally to this paper.

Abbreviations used in this paper: ARPFBE, ARP2/3-dependent FBE; CD, cytochalasin D; CIN, chronophin; COFFBE, cofilin-mediated FBE; FBE, free barbed end; fMLP, formyl-methionyl-leucyl-phenylalanine; P-cofilin, phosphorylated cofilin; Rac1N, Rac1 null neutrophil; UNCAPFBE, uncapping-mediated FBE; WT, wild-type.


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