Submitted on April 25, 2003
Accepted on May 29, 2003
Role for phosphoinositide 3-kinase in Fc
RIIA-induced platelet shape change
Kurt L Barkalow1, Herve Falet1*, Joseph E Italiano1, Andrew van Vugt2, Christopher L Carpenter2, Alan D Schreiber3, and John H Hartwig1
1 Division of Hematology, Brigham and Women's Hospital, Boston, MA, USA
2 Beth Israel Deaconess Medical Center, Boston, MA, USA
3 Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
* To whom correspondence should be addressed. E-mail: hfalet{at}rics.bwh.harvard.edu.
Platelets transform from discs to irregular spheres, grow filopodia, form ruffles, and spread on surfaces coated with anti-Fc
RIIA antibody. FcRIIA crosslinking leads to a ten-fold increase in actin filament barbed end exposure and robust actin assembly. Activation of the small GTPases Rac and Cdc42 follows FcRIIA crosslinking. Shape change, actin filament barbed end exposure and quantifiable actin assembly require phosphoinositide (PI) 3-kinase activity and a rise in intracellular calcium. PI 3-kinase inhibition blocks activation of Rac, but not of Cdc42, and diminishes the association of Arp2/3 complex and CapZ with polymerized actin. Furthermore, addition of constitutively active D3-phosphorylated ppIs or recombinant PI 3-kinase subunits to octylglucoside-permeablized platelets elicits actin filament barbed end exposure by releasing gelsolin and CapZ from the cytoskeleton. Our findings place PI 3-kinase activity upstream of Rac, gelsolin and Arp2/3 complex activation induced by FcRIIA and clearly distinguish the FcRIIA signaling pathway to actin filament assembly from the thrombin receptor PAR-1 pathway.
